Pregnant?

So my fiance is in the Marine Corps and stationed in North Carolina. I just finished college and am working in Ohio. He came home for memorial day weekend and we had sex and I let him cum inside me for the first time (twice in as many days). I'm on the pill so I wasn't worried but my work schedule became hectic just afterwards and I forgot to take my pill for 3 days. I took all the pills I missed and the one for that day (4 pills). But since then I've been experiencing spotting, brown discharge and cramps. I thought my period was coming early because I'm expecting it next week. But could the spotting be implantation? I've bought tests to take but don't know how long I should wait to take it.