Foul taste in mouth

Sierra • Hope you're having a good day :)
I woke up with a foul taste in my mouth which my friend described as old Cheerios because she has stomach problems but we do not have same symptoms. 
I have had bloating, constipation for a few days then dirrhea for a few days. The foul taste happens when I have these little burps which happen frequently throughout the day.
My period is in 2 days if that matters any
Does anybody know what this is?