meds for back pain?

Hi, I have lower back muscle pain...pretty bad...(probably stemmed from lifting boxes while shopping) went to Dr. and he prescribed flexeril (muscle relaxer) and a steroid pack that is about a week long and tapers off. Sent a message asking my Dr. if it is OK to take these with my UC and being in my first flare....but they may not get back to me soon with the Holiday....Does anyone have any advice...is it OK to take these? I did start taking half doses of the flexeril...yesterday....stomach was upset last night but that could have been from anything....Didn't pick up the steroid yet from the pharmacy but will today...Also, is it bad to take a steroid for this short time? Will it help or hurt my flare?
Thanks!

Thank you. That is what I was thinking too.