Two day periods?!?

I've been ttc since May. I used to have four day periods, and was pretty regular. This time, I was a few days late and it only lasted two days, one of which was heavy. Has anyone had a similar issue? Should I be concerned about it? I figure it can't be implantation bleeding, because of the heavy day. Plus, I took a test after I was two days late...couldn't wait...bfn. hope everyone's doing well and staying positive!!