Period or implantation bleeding?

So last night my SO said my boobs are starting to look bigger and my breasts have been sore and I've been getting really nauseas. Didn't think much of the nausea because I always get nauseas from my birth control. But then I was thinking about it and my last period was very very light and only 3 days. I never even filled a tampon. Could that have been implantation bleeding? Thanks! I hope I'm not pregnant!