Advice? Please!

Ka
My husband and I have been TTC for about a year now.  This month I had peak fertility smiley on 2/3.  We BD'd before and during fertile window.  AF was due the 17th but yesterday morning I started having very dark brown spotting with horrible cramps by that night I had no spotting with light cramps.  Took HPT yesterday there was a very faint line.  
​This morning I started having horrible cramps again, like fetal position, heating pad and Tylenol bad. With no relief. And very dark-red/brown spotting again.  Took another HPT and it was very negative. I plan on calling my Dr. ASAP Monday morning.  But I'm really freaked out I never spot before I start nor do I cramp this bad at all.  If anyone has experienced this or might know something I would really appreciate it! If this had happened before I could understand it. But it is new and very strange for me. Thanks