@Jolease When mine was at its worst, and before I knew what the problem was or how to intervene early, everything aggravated it. I do mean everything!!!! I couldn't even lay on that side at night.
Biking and going down stairs were the worst though.

Walking wasn't as bad, but it didn't necessarily feel good either. I honestly can't remember if going upstairs was painful or not (??)----it was too long ago with that first debilitating flare up (17 yrs maybe ?). Mine was initiated from too much sitting, too much bike riding (should have been mixing things up), plus no stretching. Now I know I have a very tight right hip, and a very loose left hip due to an accident in college----thus everything on the right side of my body has more tension/stress in it, and suffers the most with any injury/stressor.
I was also teaching full time at a college, and I was preparing all of my courses from scratch. It required a lot of sitting in one spot for hours, putting together notes and slides. Now, I still notice prolonged periods of sitting will make it tight, and that's a night I have to stretch and foam roll the IT Band a lot.
Lastly, and I don't mean to be negative, but I needed PT for 3-4 wks before I saw any lasting relief. It was a long progress with slow gains/improvements that could be offset by sitting too long in a car one weekend. Once we got 3-4 wks in though, I could maintain it with stretching. I didn't start rolling it until 5-6 yrs ago and find that workds faster and gets more lasting results. That's just me though. Also, IT Band PT did not hurt. It was absolutely wonderful once I got past the first 2-3 visits where the hot spots in the IT Band were so tender.
I hope you can get some lasting relief. IT Band pain can be absolutely miserable. I'm a side sleeper and simply couldn't put pressure on that side for months.
