As a paediatric Dietitian I have treated cows' milk protein allergy and weaning off AA formulas such as neonate many times. If you feel your child's diet is restrictive, and are worries about food allergys, it is really important you do get help and not just try and change things willy nilly as that can make the situation worse.
The gold standard for food allergy tests are skin prick tests (RAST testing) and your GP can refer you onto an allergy clinic for these. RAST testing prior to 5 years of age isn't always perfect-you can get lots of false positives (indicate an allergy when there isn't one) but as they are 'grades' of allergies, you can then get information on how to deal with this. I work within the food allergy clinic at Guys and St Thomas' and you will get referred to a dietitian to help you manage it so you aren't alone.
I also offer private appointments, but I would definitely recommend RAST testing (through the NHS) anyone over 2 years of age.