I think you tested too early. You had a positive OPK on the 5th, so you probably o'd on the 5th or 6th. It takes anywhere from 6-12 days for implantation to occur (so anywhere from the 11th to the 17th for you) then it takes 3 days for hCG to show up in blook tests and another 2 days for it to show up in urine (so anywhere from the 16th to the 22nd) That's what's typical, but of course everyone is differnt. But I'd say you're not out. If you are what's considered typical you wouldn't get a positive until sometime b/t the
16th to the 22nd.
good luck and don't lose hope.