You really dont have to worry. My period was always always irregualar. i started when I was 13 then I didnt het it for like 6 months after that it was always on and off, my cycle is just irregular. Im 26 now, and last year I finally went to a gynae for a checkup and the first thing they do is test for PCOS (polycystic ovarian syndrome) as an irregular period is an immediate red flag for that. However when there wasnt that, he did a blood test for diabetes, thyroid and hormones. Finally came to the conclusion that my LH hormone was too high and he put me on the pill for a year to regulate it. I also wasnt sexually active until 5 months ago, so I knew it couldnt have been pregnancy earlier.
I think since you only started your period, you dont need to worry, maybe just go to a gynae and have them check for cysts and diabetes etc.. but you already mentioned that you are not overweight so im guessing you don't have anything to worry about, you will just have an irregular cycle. Howver still go to a gynae and maybe he can put you on the pill to regulate your cycle.
Hope this helps