Help!

Sara • Have two beautiful children and am trying to have another.
Typically my periods are every month around the 18th of the month. I bleed for about four days and I have horrible mood swings, depression, very sore boobs, acne, back pain. Well today my husband and I had sex and I started bleeding, brown, dark blood but had no pain or indication my period was coming early. Does anyone have any experience with this? TIA