first of all your problem is nothing to do with the tantric sex, its due to bad toilet routine, like most men, they seem to thinki tha t going to the batthroom and sitting there for hrs on end usually with a book in hand is ok. well all your doing is trying to force something out that just wasnt ready to come out!!!! believe me if you needed the loo in the first place then you wouldnt have to do any of this.
next is that you sound like your getting consiptated, you need to look at your diet and increase your levels of fliuds preferably water intake,
and lasty stop sticking your finger up your bum its not neccessary, you might like it but its not needed
Stop trying to squeeze it out - that causes hemorrhoids. Just let your body tell you when you have to go do number two.
Dude those are not muscles, they are swollen hemorrhoids and they are caused by all your pushing and marathon toilet sessions.
You are constipated like all hell, go get some Metamucil powder and chug it with plenty of water right before bed time and your crap will be like soft serve ice cream the next day. Do that for 2-3 months and those hemorrhoids should shrink up.
Then start eating some nice high fiber cereal in the mornings and drink lots of water to remain regular. I eat Shredded Wheat cereal every morning and my crap takes about 5 seconds to get out, and its usually quite huge ( 2ft+ ) and soft. I go every morning the same time. You will probably live 5 years longer if you do this.