There are drugs you can take that may alleviate the symptoms if it's a strained muscle. Flexeril is a commonly used one that isn't addictive. Could be worth asking about to use on a trial basis since it's a few weeks out from your appointment in KC. And MRIs can see herniated discs, although even if one is found, usually nothing much is done about it other than to ride out the symptoms.
Anyway just saying, you're doing the right thing but don't get freaked out about finding something weird. BTW if you're working out you're ahead of about 90% of fissure sufferers out there :) Even when my fissure was under control, lifting weights was about as attractive of an idea to me as driving a school bus up my rear
