Why My Period Is Not Regular In Time?

my menstrual cycle has become 48+ days and it has been going on for a couple of months since my school finished..i dont know whats going on..my age is 18 and i am 165cm tall and i am 67kg.. i have gained five kilograms since my school finished but that is cause i eat and dont do much of work..last year i had typhoid four times and had stephlococcal infection and i also have irritable bowel syndrome.. please help should i go to a doctor? i am scared of the medicine they give it has many side effects..