My do i have these bumbs?

okay so i have 5 cats and my all luv to drink out the toilet . so now am getting this bumps under my leg you know by your Virgina and i never had this before until the cats came whats going on cause some of them hurt and some are just big lumps they don't really bother me unless i mess with them or something pls help i hope i dnt have anything. is it because of the seat and hoe that cats have been all over it or is it somethig else. if it is the seat how can i fix it