Period every other month?

I’m nearly seventeen and I’m fairly certain I got my first period just after I turned thirteen. From the very start I have only ever gotten my period every other month and at the start my mom said that was normal and I would get regular soon but it’s been nearly four years and I’m still off. Somtimes I’ll get my normal period and it won’t be to heavy but it will be really light for a few days, normal for a few and then light and drawn out for a while so it ends up lasting like a week and a half, and then the next month I might get a few days of practically nothing or nothing at all, and then it will coming sometime during the month after that but I’ve never been good at keeping track of it. I never get cramps or break outs or anything like that and I usually never feel sick or bloated so it’s very strange and I know I should get a PAP test or something like that but I really don’t want to get that done yet so I was hoping someone might have an idea as to why my period is so funny. Thanks! : )