STD or Hemorroids?

Hi I'm a gay male who has anal sex from time to time. My last partner was rather large (8 inch) and often left me sore. Even though there are no visual symptoms to this phenomenon I see. Whenever I try anal stimulation it feels like the inside of my asshole is on fire. I can so much as insert my smallest finger in an inch without feeling excruciating pain from the inside. I haven't been able to have sex in weeks and have no idea what is going on. I'm having no bleeding and have no idea why I'm having such pain. I never have had it before.