heavy spotting during exercise

Jenny
Quick backstory.  I had a miscarriage last August at 8 weeks.  Before getting pregnant I was super in shape. I had a personal trainer. I could run a 5k on a lunch break etc etc.  after the miscarriage I basically fell into depression, stopped working out and gained weight 🤦🏼‍♀️
Ever since that miscarriage every time I get a good hard workout in...I start spotting.  Not just like when I wipe I see brown. But like bright red enough to wear a pad or tampon.  I get cramps and all. 
What is happening??? Has anyone else been through this?? 
I plan on calling the doctor in the morning but until then any advice?