This just happened to me as well but it went away and I have been fine since
I was the same it's from sex
Go to ur obgyn first thing tomorrow. Sometimes spotting can be irritation or can be a signal of miscarriage. I personally started with spottinh and it increased. Dont freak out, just go to the obgyn tk be on the safe side.
It's very common for sex to cause spotting due to it irritating your cervix if it lasts more than a day contact your obgyn and see what they suggest doing just try relaxing with your feet up till it stops