Pregnant or Period?

Since my wisdom tooth surgery 2 weeks ago, I've been picky and craving certain foods. There were days I would eat 1 meal and a snack. I had sex Saturday and my period starts 31 of this month. This morning I took a shower, had some cramping, And noticed blood going down my leg. So after my shower I put a liner on my underwear but noticed the flow wasn't enough to use a tampon... This flow is light and my period is isually a normal flow. Am I pregnant or is my period starting and is light due to lack of nutrients???