we have have been trying and we have had no luck for the past year and half! so cross your fingers and pray that i am!!!
You can take it the first day of your missed period (even a couple days before that depending on the brand). I would say go get a pregnancy test now and see what it says since it should be accurate. Stress can cause your period to be late as well so if you've been under any stress lately than that could be why you are late. Are you trying to get pregnant?
It depends on the sensitivity of the test. Go to www.peeonastick.com. It shows the different HCG levels popular store brand tests for. It also mentions average HCG levels in pregnancy. Sounds like you are 18DPO. Most people have different experiences. I personally always trust first response. I got a positive 2 days before my expected period. However, some women get a positive way earlier. I think 4 days after your period is expected will be plenty of time to see a positive if you are in fact pregnant. Good Luck, keep us posted!