Could it be twins??

I am 6 weeks and 3 days today. I have gone up 2 cup sizes already in a bra, I have never felt so tired in my life! This is my second, and I never felt this sick, tired, fatigued, etc with my son. Everyone keeps joking, "Oh, it could be twins!" The fact that I am already in maternity clothes, and look 3 months+ I'm starting to wonder! Has anyone ever had "symptoms" making you think you were having twins?