This is my story haven't had sex since February 2014, had sex with an ex April 24th, 2014, period due May 4th( come regularly on the 4th of every month) missed period , took two pregnancy test on the 4th and 8th negative. Started spotting on May 12th, very light and brown with cramps. Could this be implantation bleeding? Does having sex right before my period interfere with when I would get implantation bleeding? Could I be pregnant ? And if so when should I be able to test?

Yes you could be pregnant, and yes it interferes.

You need to wait till next period is due. And test

You are testing too early.

This is my story haven't had sex since February 2014, had sex with an ex April 24th, 2014, period due May 4th( come regularly on the 4th of every month) missed period , took two pregnancy test on the 4th and 8th negative. Started spotting on May 12th, very light and brown with cramps. Could this be implantation bleeding? Does having sex right before my period interfere with when I would get implantation bleeding? Could I be pregnant ? And if so when should I be able to test?

For some women, sex right before a period may alter it slightly once in awhile, but it won't interfere with implantation bleeding should you become pregnant. If you happen to notice implantation bleeding, it usually occurs about 6-10 days after ovulation or about a week to just before a period is due. You can, however, have some spotting or light bleeding in early pregnancy.

Since your period was due the 4th, maybe try another test in about a week or wait and see what happens when you would expect your period for June.

Sometimes a period will just be off... it could come a bit sooner or later than expected, it could be lighter or heavier once in awhile, or you may skip a period now and then.