Implantation!

I had ovulated around day 10/11I am very regular with ovulating and had all the symptoms. Intercourse occurred day 10,11,12 and (I think) 13. On day 19 I started spotting. Here is where it is confusing I have been spotting Day 19 - today- Day 27. It red with occasional pink/brown. I had cramping on Day 19 ( none since) and back pain Day 20-23. I am very regular with my cycle. I should start my cycle Day 29 (two day). I have had no cramping, which I normally do.  This is driving me crazy!!! I know it is to early to test and I feel this spotting has lasted too long to be implantation. Note: this is super light spotting. Only visible by wiping... no tampon/pant liner needed. Thoughts????