I strained a side glute thingy swinging a leg over my bike once; straddling the top tube or riding I was fine, but very difficult to get on/off, or do anything once off the bike other than lie down. Couldn't sit.

Lots of stretching fixed it. Lower saddle would have made mounting the bike easier but not much else. Maybe this has nothing do w/ your situation, but in general more stretching fixes all my back ills.