Gender and emotions

So my 5 year old son has been acting really attached and really emotional lately. This is his second week back at school from winter break and he's cried everyday before bed. When I ask what's wrong he says he misses his teacher (who is on maternity leave) but I feel like it's me being pregnant that is bothering him but I asked him and he said no. Another thing I was thinking it could be is he just got used to staying home with me on winter break....has anyone else heard if your having the same sex that it could cause your current child to be emotinal and more attached to you?