I have been eating dairy, soy, oat, and wheat free for seven months now and it is challenging but very doable. My daughter has severe allergies to both dairy and soy, wheat and oats, since I am breastfeeding I must go without them as well. You pretty much have to eat all whole foods, nothing processed because dairy and soy especially are in just about everything.
Reading labels is a must. There are hidden ingrediants in lots of foods and spices. Canned vegetable stock, chicken stock, mayonaise, seasoning salts, marinades, canned soups. Everything has to made from scratch.... which can be a hassle with three little kids running around.
I still haven't found a salad dressing that is allergy friendly, so I just make my own vinagrette in small batches to keep in the fridge. When I crave something salty I grab a pickle, or something creamy I reach for avacados. No one seems to understand just how difficult it is because they never read labels until they have to go without. Good luck to you!