miscarriage confusion, please help!!!

So I started what was thought to be my period almost 3 weeks ago, and had it for 15 days. I tried talking to my doctor and she just shrugged it off and told me to just keep taking my normal birth control. Around day 12 of the bleeding I was hospitalized for unrelated reasons and they asked if I thought I was having a miscarriage and did a pregnancy test, which came out negative. It finally stopped a couple of days ago, but today I found light pink blood and pieces of tissue when I went to the restroom. I don't know if I was pregnant, and no doctors seem to be taking me seriously and now I'm just getting very frustrated to not know what's happening with my body. Could this be a miscarriage?