those who have had a placenta abruption

I know this is a hard topic and i'm sorry in advance.
For those of you who have had a placenta abruption, what happened? What were your symptoms? 
Google just says bleeding is the first sign. The problem is, i'm 21 weeks with a subchronic hemmorage, so i've been having bleeding for a long time, with quite a few random gushes of blood. 
So im wondering, how much is the bleeding when it happens? Is it bright red? Pain, cramps? I'm just trying to prepare myself so I know what to expect. My doctor said he was worried the bleeding im having could cause it to happen but did not explain what to look for. I see him again in 2 weeks so I would like to educate myself as much on it as possible.
I have bright red and brown bleeding already. I actually have to wear the protective underwear (adult diapers) because of it. Thank you in advance for anyone who can help me out!