How much discharge is normal?

pathfindermon

Sorry if this is TMI- but I have been having a lot of discharge for the last few weeks.  It is watery and is sometimes a little yellow.  Sometimes I even need to change my underwear b/c of it.  Has anyone else had this happening?  I'm 20 weeks now.  I did ask my doctor about it but she didn't really give me any answers.  I guess I'm wondering how much discharge is normal?

TIA!!!!!