strange period

I am very skinny and I've been exercising a lot for a few months, lose fat (thought I didn't have much to lose) and gained muscles.

For 3 months my period is coming earlier and this month wasn't different but I'm cramping a lot and almost haven't seen blood, which is strange since I have a really heavy flow.

could it be because I'm exercising too much? is this normal or should I go to my gynecologist?