Period came on March 7, went off March 14. I had sex the week after on the 23rd. My period should have came on April 4th. I waited to April 7th and had a pregnancy test that came out negative. Last week I had cramps and implantation bleeding. What to do?

You need to wait until your period is two weeks late, then test using the first urine of the morning.

It's possible what you thought was implantation bleeding was your period, just off from your norm. Or it could have been an off ovulation. Wait a bit longer, and if you still don't have a regular period, try another pregnancy test, following the directions carefully.

Most pregnancy tests increase in accuracy the further you get from your due date. So 3 days is too soon. Try again next week.

I will agree, you assume implantation bleeding, it may be light bleeding for a dozen reasons. A light period is one of them. Infections, stress and other issues can cause it also.

As others have mentioned, you tested too early, two weeks after a missed period is a good time to start trying. Make sure it is always in the morning, after you wake up, with first urine of the day.