Hello doctor i am 29 year old i feel stiffness in left side of my lower abdomen after masturbating i also get constipation ,my penis also gets tight.

My guess is ...: ... you are simply experiencing the sensation of mild muscle tightness after the abdominal muscles contract during orgasm. I don't think that would actually lead to constipation--the constipation is likely due to other factors. Masturbation is normal as long as it does not impair your experience of interactive sexual activity. Good wishes:)