Need some help!!!

Alicia • My husband and I married in Sept 2014 and have been trying to conceive since. We did get pregnant in Feb 2015 and miscarried at 7.3 weeks. We hope to be successful again.
So currently I'm 7 dpo. I had a successful ovulation. I'm on second month of clomid this was just an extra helper I guess you could say from my doctor. Here is the kicker, I know around 5 to 7 dpo is when implantation happens. It's very rare that it can happen around day 4 to 5. I refuse to buy hcg tests because all I do is waste them and non stop test. But i decided today to take an ovulation test and it was as negative as negative could be. Like the second line wasn't even visible. I have been doing some reading and people say opks can act like a pregnant test. Am I out this month. I really thought we did it this month. I was so positive that I was going to get pregnant but the close we get to my aunt flow I'm feeling that same loss I feel every month. Do opks pick up 7dpo? Or am I not being patient??? Helpful answers please. My husband and I have been trying a year. We did get pregnant and lost our baby at 7 weeks and have been out of luck since.