I am feeling fine except that my lower left side muscle area of my back aches enough to take advil. am i having a heart attack?

Unusual location: The lower left back is an unusual location to have pain from a myocardial infarction (heart attack). However, that doesn't mean that something is not wrong - pain is usually a warning sign. If you've not had any trauma, then I suppose muscle strains or back injury is out the question. The colon (colitis) or kidneys (ureter infection/stone) or even AAA (aneurysm) can cause it. Talk to your doctor.