Missed period... But constant blood!

Shannon
I missed my period, no I'm not pregnant, last month and then thought it came early just before Christmas <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">Eve</a>. However, it hasn't stopped. It's only light spotting (which for someone was heavy as me is beyond bizarre) but has now went on for 3 weeks and gets slightly heavier after sex with my partner! 
Im so confused, I've been to the doctor and they just brushed it off.
I also have a very very painful left breast even if someone just brushes by I'm in agony!