hello and welcome im not a doctor but a suppporter for the forum.
from what you descibe your purple spots sound like you have piles and sometimes they can form like a small bunch of grapes. heamarroids are the medical term.
they are caused by constipation and i would suggest you use a stool softener like senokot or dulcolax to make going to toilet bit easier.
i too have to do this and at one point if one bursts i get a bit of relief. i also use an anal cream which can shrink them and helps if itch developes.
if they persists see your doctor as they can become painful even though you don,t feel pain now.
your tummy pains are with you being constipated so you need to find out why?
hope this helps take care.