The first step is to be sure that the diagnosis is indeed accurate. It is not clear how these allergies were established. It is not a very common problem. Contact your doctor
There is an excellent book I bought years ago titled "Good Recipes for Hard Times - a cookbook for people on a limited budget" by Louise Newton. Perhaps your library still has a copy. I searched on www.half.com and the used prices are pretty outrageous.
Her first requirement, when money is short (quote follows): "first you must fill your people up, and then you must give them the best nutrition possible with the money you have.....[all the dishes] come down to starches with the addition of whatever else [is] available.
The most expensive thing you need in order to have good nutrition if protein. The nutrition experts say that if you drink a quart of milk a day you have more than half the protein you need. The best way to do this is buy powdered milk. The less money you have, the more important it is to have that milk...
If you wish, you can vary the milk with other dairy products. An ounce of cheese is about equivalent to a glass of milk in protein and doesn't cost a great deal more. And one egg contains as much protein as 2/3 of a glass of milk; eggs are the next best buy to milk, I think, because they combine so well with cheap things to make delicious dishes....A good rule of thumb is to have enough of them to give us two thirds of the protein we need for the day. The rest can be gotten from the four basic starches [beans, rice, cornmeal and grits, and flour]."
Why are you restricted from crackers and bread? Are you diabetic? If your nutritionist is a chiropractor and is telling you that you have to steer clear of yeast, good luck, because yeast is everywhere. Most normal people have a few yeasts in their feces. I know because I'm a microbiologist and have see it grow in cultures and have seen it under the microscope. It usually only causes a problem if the patient is immunocompromised, i.e. is HIV positive, is a cancer or renal (kidney) patient. That being said, I am obviously in no position to tell you to go off this diet; but I am in the position to say that I'm skeptical. You are missing out on many good things to eat that are cheap and filling and good for you (if you go with wheat bread and avoid white bread and white crackers).
Teenage boys need nutritious food that fills them up. Fast food is not the answer. It's expensive to boot. Go to the library and look up some basic recipes with beans. Libraries have tons of cookbooks and they are free! Chile con carne is good if you cut your meat in half and dump in lots of beans. I make mine with 1/2 pound of meat and three cans of beans. You can hardly tell the difference, and the fiber will help to fill him up. Go with oatmeal instead of packaged cereal. You can get lots of bang for your buck with real store brand oatmeal. The more processed a food is, the more it's going to cost.
Lentils are extremely filling and good. If you've never tried them you're missing something. They are bland and you can season them up many different ways.
Good luck - hope this helps.