Implantation bleeding and cramps?

My SO and I have had unprotected sex 5 times this cycle, including last night. 
This morning I noticed blood on my panties. This has never happened before, and my period isn't due for another 9 days! Could it be implantation bleeding?
I don't know if it relates, but about 5 days ago I was having extremely painful cramps on and off for a few days. 
 
My cycle is about 38 days and he came in me on my cycle day 12, 14, 15, 16, and 28. I'm on day 29 now.