I have problem with my 10 plus year old female cat can anyone help me? she keeps pulling her hair out help me?

my cat recently had to visit the vet, she had some bad teeth and they pulled like 5 - 6 of them she did well... they checked her all over and even did blood work she was healthy for her age, after like a week she was eating very good. Then, she started pulling balls of her hair out from both sides of her body until now almost bald in places. I took her back to same vet who claimed maybe she got reaction to flea bite or something and he have her flea medicine. We never found a flea on her but I went along with vet. He then gave her allergy shot just in case she had reaction to vaccines she had. Its been almost two months and she still is pulling her hair out when she grooms...now she is starting to do it in more locations and it worries me I dont know what to do. She never did this before going to vet and having her teeth pulled can anyone help? thanks