What Causes Swollen Pharynx Along With Ulceration?

I have swollen pharynx on the left side. One ulceraton is there. At the back of it small vesicles like thing is present on both left and right side. But it is little bit swollen on the left side. Doctor has given me only antiseptic and pain relieving gel to apply on it. I am afraid it could be a case of benign tumor. Kindly advise.