Strep usually looks red with white pus lying on the tonsils or pharynx. Ulcers can be from viruses, we call them aphthous ulcers. If it worsens or persists have a doc check it out.
It could be strep, it could also be an infection in your throat from your sinuses. I get it all the time. You should get it checked out, and try drinking ice cold drinks if it hurts.