Experiences w/ pes anserine bursitis?

I started having knee pain seemingly out of nowhere about 3 days after my first half marathon (no issues leading up to or during the race whatsoever, hit my goal time of sub-2hrs), so a little over 2 weeks ago. I went to a physical therapist who specializes in running injuries and he suspected pes anserine bursitis (pain is in that exact spot below the knee) but suggested an MRI/x-rays to rule out a stress fracture or ligament issue. Went to ortho clinic, got x-rays which were normal, the ortho also suspected PA bursitis and said to give it 3 weeks of PT and no running before she would order an MRI.

Long story short, I’ve been doing all my PT exercises and stretching, yoga, strength training and only doing Peloton low-impact spin classes for cardio (no pain when biking). The knee isn’t really improving—granted, it doesn’t hurt to walk, but I did a very quick test jog yesterday and again today and I feel like I can’t put weight on that leg when I move from walk to jog. Feels almost like the knee is going to give out and I can’t run “normally” even when I try to ignore the pain.

It’s been 11 days since the first PT appointment and 2 weeks since I last ran. Is it normal for this kind of bursitis to take this long to improve? And for it to feel like the knee is going to give out / not be able to run at all without a major limp—or should I try to get an MRI ASAP?