Wow! You've made amazing progress -- congratulations! I'm not 100% sure that I understand your question, but it sounds like you're at the point where you might consider having a body fat test done.
The most accurate body fat tests cost about $50-$100 and involve actually having someone test you (as opposed to buying a home scale with BF % capabilities or using online estimators). You'll go to a gym or doctors office and they can "pinch an inch" with calipers, do an x-ray style body scan or you can get dunked in a pool of water (I know, right?). Since I'm assuming you didn't do this type of test at the outset of your plan you won't really know how your body composition has changed over time, but it will be the best way to figure out where you're at now. You might find it easier to decide what goals are most important from that point.
Not to be a downer, but it is possible that you have lost both muscle and body fat over the past few months, which is the most likely cause of such successful weight loss. I suspect that you already had reasonable muscle mass underneath the fat and it is only now showing through, giving you the sense of building when you may actually have had a loss (which isn't really a huge deal at this point since you don't know where you are until you have the BF% done). It is very difficult for women to gain serious amounts of muscle over the time period you describe. Gaining (or even just maintaining) muscle while losing fat is pretty much the "holy grail" of fitness.
IMHO, you should prioritize maintenance of the muscle you have over getting the scale to read 120. The reason is outwardly simple, but in reality very complicated: muscle is more compact than fat (i.e. you can weigh 140 and still look as slim as others weighing 120 or lower) and it burns lots of calories just to maintain itself. The more muscle mass you have, the more you can eat without gaining weight. Got it? Sometimes this effect is overstated, but certainly your body burns a lot "hotter" at 140 lbs and 18% body fat than it does at 140 lbs and 30% body fat. Ya know those skinny athletic friends that can eat and drink all they want while staying skinny and athletic?...Yeah, that's what I'm talking about. This is why, at some point anyway, the scale is irrelevant. If you diet and exercise down just to become skinny-fat (read: 140lbs, 30% bf), your metabolism will take a hit and you will gain the weight back more easily while eating fewer calories than you did before.
Bottom line: For someone as successful at losing weight as you have been, it might be a pretty simple matter to just get down to 120, but it will be much more challenging to do that while maintaining muscle and your ability to "burn" at a higher rate throughout the day.
As you mention, your body has likely grown used to you usual strength training routine. I would hire a good trainer or check out New Rules of Lifting for Women by Lou Schuler in order to switch up your plan. I HIGHLY recommend this book -- it completely changed the way I thought about my time at the gym. Contrary to what you might think, yoga will not lengthen your muscles (the overall shape of your muscle can't be changed in the way that women's fitness magazines want you to think). However, switching over to a yoga-based routine for a little while might challenge you in different ways than lunges do and you might see some strength and flexibility gains. There are a zillion different routines out there, so don't get discouraged. You do not have to get burnt out on your routine to be successful.
In addition to having your % body fat accurately measured and possibly switching up your routine at the gym, you'll really need to focus on your diet. I'd actually argue that this is the #1 thing to concentrate on if you're trying to drop body fat. You know that saying that washboard abs are made in the kitchen? Well, its true. You should be eating really clean with lots of lean protein and fresh veggies. Once you do that, your body composition will definitely change. It just takes dedication and a little obsession.
Finally, remember this: what you're doing already is obviously working. You may just want to tweak your routine if you want to keep dropping weight. You can probably keep dropping pounds for a long time, its just up to you to find a weight/pants size/bf % that you're happy with and how obsessed about it you want to get. Take a long hard look at what's most important to you when it comes to diet/nutrition/fitness. Its okay if your original goal changes -- after all even in maintenance your weight, strength, endurance and even your body fat will fluctuate constantly -- this is all just a big experiment, right? Its going to take some time to figure out what you want and what will work for you in the long run.
Oh, and make sure you take this opportunity to enjoy those size 8 jeans a little. Even if you drop some more weight or BF, this summer has got to seem a whole lot different from January!! Amazing work! Keep it up!!
P.S. Holy cow! This post got long. Never let me write late at night again.... Ugh!