Implantation pain?? Anyone had this?

my last periods first day was the 15th june and have been trying for a baby ever since. We had intercourse on the day before my period and on the 17th, 20th, 23rd, 25th and the 26th and now today which is the 28th I feel like I feel when im going to have a period. Not necessarily stomach cramps but I feel achy and have a really bad lower back. Has anyone had this? Could this be implantation pain or is it too soon. Its defiantly to soon for my period as im not due till around the 13th-14th of july