I am not sure, but think I read somewhere that an OPK can read a pregnancy and give a positive result.
It's well worth going to an ob-gyn (not the ER) this week and getting an ultrasound. They will give you a gestational age count, which is the one like 6 weeks 2 days. What it means is a number of weeks, computed from the size of the embryo, since the assumed first day of your last period. So if a doc tells you that your GA is 6 weeks 2 days, what he or she is saying is that you conceived about 4 weeks 2 days ago.
From the ultrasound, they should also be able to give you an estimated due date. You can count back on a calendar 266 days from that date to get to an estimated date of conception.
If you get an ultrasound and the doctor or the tech says "You're 7 weeks pregnant," just keep in mind he or she is not saying you are 7 weeks from conception. All medical counts begin on the first day of the last period, or the imputed first day of the last period if the woman doesn't know when it is or has irregular cycles.