AF question (TMI Alert!!!)

So I am cd2 and normal for me is heavy flow cd1&2 and then light flow for cd3-4 spotting cd5. AF has been very light this cycle. I keep waiting for it to get heavy but it's not. It is, however, very thin. I have been going through tampons like crazy because the blood is so thin. There is very little blood but it's so watery it's like I am peeing my pants. I don't get it. This has never happened to me before. I just had to change my pants and the area with the watery blood smelled like ammonia. So I wiped with TP and smelled the blood and no ammonia smell. I am kind of freaking out a little bit. Has anyone ever experienced this? Please help if you can....Thank you!