implantation or period?! please help.

Whitney
So I got my iud (mirena) out on dec 12, this past couple of weeks I've been tired and my boobs have become sore when running down stairs. This morning I had a sharp pain in my left side almost like a cramp and then went away after 5 min. Could this be implantation bleeding or just my period, my boyfriend and I have been ttc. Please please help!