is this an "internal" spasm, that you feel....or superficial muscle spasm? if the latter i would think nerve from your back, and even the internal might be that as well......if it is the former, i would think gall bladder, knew someone once who had gall bladder issues from late toddlerhood into teenage, before it was finally figured out....you might investigate diet for gall bladder disease and try that.....cant hurt and dont need a doc.........that said, if this is a pain that comes and goes, not a true spasm feeling..and if you happen to be female, + this started after hm, after certain age.....you could check into a variant of PID
good luck