Baby kicks?

I'm 16 weeks and 3 days and yesterday I could of swore I felt baby kicks. Not just little flutters, but 2 kicks! I wasn't even thinking about the baby or anything and I felt a kick in my stomach and I've never experienced something like that before! So could have it been the baby? I mean what else can it be I never felt that before! And today I'm not feeling anything at all but yesterday I did so I'm worried ?