Really weird Letrozole experience. Any advice?

I have lean PCOS, early 30s normal BMI. cycles vary wildly, but last three have been between 48-54 days.

started 2.5mg letrozole from CD3 to CD7. Had scant spotting, didn’t think anything of it. Transvaginal US on CD13 showed very small follicles and a uterine lining of 7mm. They asked me to restart Letrozole at 5mg from CD13 to CD17. Had lots of bright red spotting, enough to soak a liner on CD17.

Mild spotting continued today (CD18). went for a scan. No uterine lining found…! They couldn’t even measure it. found two follicles measuring 12mm. Bloods show LH is surging (43) and we’ve been advised to have sex next four days, though they don’t expect it to work.

this is such an odd experience, the clinic has no idea what is happening. Anyone have any thoughts?