Help pleasssse.

I've been ttc for 14 months and have never had a positive opk. I'm on my 2nd round of clomid. Last night I got a decently dark opk but not dark enough to be positive (it was only cd 10). Then this morning, it was back to barely visible. Any idea why this could be? I didn't think it should go lighter without ovulation having occurred. Any help is so, so appreciated.