Could I be pregnant?

Im 24 years old and I had some holiday romance with a 21 year old friend of mine who is in the Marines. We haven’t seen each other in 5 months before our holiday in LA and Vegas so we couldn’t keep our hands off each other.

I’m on the pill, and I let him finish in me. However, when I came home last Thursday, I’ve been feeling depressed. I had to force myself to get out of bed, shower, etc. The last two days, I missed my pills and I took the pill for the day and the two I missed today. I’m spotting a little bit, but I read something called implantation bleeding. Could I be pregnant? I don’t know if he’s coming home after he gets out of the Marines (he’s stationed in Hawaii and he told me he might stay there after he gets out).