HELP!

I've always had an irregular period, BUT I've always received one. I missed my period last month, only to get a 9 day period this month. Usually I have heavy periods with no cramps. This period was very light with bright red blood mixed with clear mucus & cramps here & there. I have scheduled a dr's appointment but does anyone have any insight on what's going on? Or have you experienced anything like this? I know everyone is different but feedback is greatly appreciated!