I have ulcers in the back of my throat for over 3 months..

I went to my doctor about it because I have ulcers in the back of my throat and he said there's no infection,didn't give me anything and sent me on my way.. He had a very dull light shining in the back of my throat so it was hard to see,it's even hard for me to see so I have to use the flash light on my iPhone.. It's been 3-4 months now and they are still there,the top of my mouth is white and it's been like this for 3-4 months.. My doctor is stupid!! I don't know if this has anything to due with it but I do drink a nice bit of pepsi but I do not drink a bottle a day.. When it was happening my throat would be sore when I woke up but now I have no problems but it's still there.