I guess just trying cutting down to 1, and then cutting them out altogether if it's bothering you. You can definitely get used to the taste, beverages now taste better to me that they're not diluted with the sweetness. Do you actually want to give up coffee? maybe replace some of your coffee with other beverages.
Too much sweetener can give you diarrhea and lead to dehydration, headache, this happened to me once when i had a bar of diabetic chocoalate, never again. Oh and once when i was younger and had too much chewing gum lol. Too much phenylaline can be bad for you and cause other symptoms >.<