3 months

My son will be 3 months in 2 weeks. Since he's been born I've been sick 3 or 4 times. Before I had him I seriously never ever got sick, ever. Is it a 'thing' or possible that being pregnant ruins or lowers your immune system? Or getting not as much sleep as before contributes to it? 
Any other women who have experienced this?! 
I'm sick of being sick!!!