What Causes Constipation, Mild Headache And Lower Abdominal Pain?

3 weeks ago I had an ice cream which I felt right after eating it that something went wrong! So I had this very very light fever (Or at least I feel hot at the back of my eyes) and my habit for using restroom changed! Like I use to poop at least twice a day but now it doesnt matter how much I eat, eat either doesnt come or when it comes, right before having it, my lower stomach hurt a little bit! I also am feeling a little tired all the time! and have very light light headache at the back of my head! this situation went away couple of days ago for two days, but again it came back!