Not sure if it causes a false positive but the trigger shot will induce ovulation to happen about 36 hours later...I had those same concerns and asked my RE about it. She pretty much guaranteed me that you'd ovulate anywhere from 36-40 hours after the trigger.
I think the stim meds cause crazy not true reactions in the OPk, I wouldnt trust them if you had the meds/
I read the insert from my opk and it does say that meds with hcg or LH will give a false positive.
I had an hcg trigger shot on saturday and took an opk yesterday just to see what a no kidding positive would look like, and it was WAY darker than anything I had ever seen before.
Good luck with your IUI.. I had mine this morning so I'm not far behind you!!
Yeah I didn't think that it was accurate but this is my first time using the trigger. My temps went up too according to fertility friend I am 3 dpo right now. Good luck!!! I really hope we can share our BFP's!!! :)