have a small lump on anus.

hi i have a small lump on anus. its about the size of a pea. i dont get blood on my stool neither does it hurt when i pass them. it looks purpley and seems to flare up when i touch it or when i play football on sundays. im 18 and not sure what it could be. i think i used to wipe my anus too hard because i would get small amounts of blood on the toilet roll and it felt like a cut( this happend a few times). ive had it for about a week. when i touch it it doesnt feel hard or asif its full of fluid it just goes back into the skin. when i open my anus it seems to go in slightly or maybe coming out. it hasnt got bigger in the time ive had it it just got smaller then it went back to the same size but it hasnt got bigger. and now it seems to change size everytime i see it for example ill look at it and it will look like its nearly gone very small lump and doesnt look like its going into/out of my anus and then the next time it does? any help would be appriciated. im 1