Spotting -- help!

I had a positive opk Sunday and my husband and I had a lot of sex last week in my fertile window. Some spotting after sex is normal for me. I also had some pain Saturday and Sunday on my right side which I assumed was ovulation.. Today I've had some heavy spotting throughout the day - I've had to chance my panty liner twice and use a tampon for it since I've been home from work (maybe 4 hours). Heavier than normal spotting definitely. No cramps, no clots, just watery bright red blood. Period is supposed to start the 27 or 28. Thoughts??