Positive opk cd7 in cycle after 3rd unsuccessful IUI

[Rumum]

I've just had 3rd IUI and was unsuccessful again. I'm 40 and have been ttc for approaching 2 years. Have had one cm after natural cycle and one cm after iui 1. Will now probably move onto IVF but was hoping to have a natural try this month. Did an opk on Sun (cd7) and it was +. This is very unusual. Usually don't get + until cd 12 or 13. It's still positive today (mon). Just wondering if it's possible to have a mature follicle so early on or if my body has just gone crazy from all the hormones I've been pumping into it! Would really appreciate any input!