Right, I had this issue, could not shit, 3 day binges, and then the 4th day was not a pleasant experience of making up for it.
I dont think i got pain but i never notice or give a shit about pain when im high so im not sure.
The proper recommendation would be to see a doctor perhaps but you are probably getting meth paranoid and if you have eaten as little as likely during those 4 days, you should be ok in theory, until you comedown, when it will make itself known, i was fine with the same time frames. But im not sure, ask a medical professional.
What has worked for me:
2 things.
1. Magnesium supplemented before and during made sure it came normally daily, no issues, and as a bonus it is a oddly enjoyable but strange experience as well, like giving birth to a perhaps. Anyways, i originally used magnesium in the form of constipation tonic as its recommended for meth and thats all i had but the proper mag tablets have also been working as well.
2. It also seems to be a mental and perhaps body stiffness thing. What i have found is that it wont request attention if you are meth focused on other shit but if you go and sit down, relax and maybe encourage it with some tender, kind or soothing words or thoughts, it tends to start working. Im not joking either, you sorta have to chill and change positions, relax, concentrate etc.
It becomes this process with extra requirements and mental focus, similar to how taking a piss is far more complicated then usual. The key usually is to relax. On meth you want to dominate and force everything to your will, obey or be destroyed, but as with the stim erection and taking a piss, on meth you need to relax instead of what you normally do sober.
I hope you shit like champ shortly man really, and i am going to now evaluate how things got this bad in my life, talking in detail about shitting on a forum, high as fuk on a Sunday morning, alone at home, no friends, no cat, nobody to hold me while i cry... Only one cure for reality, more sweet sweet crystal goodness...