Im pregnant..Why is my male dog so aggressive towards me all of a sudden?

My husband had a dog before I moved in with him. He's a bull mastiff / german shepard mix so hes a big dog. When I first moved in he was a very loving and protective dog and never did any of these recent behaviors. I also brought with me my female dog who is a puggle and they get along great, hes very good at sharing with her. I am now 8 months pregnant and for the past month he has gotten very aggressive towards me. He wont jump on the bed with me anymore, he growls and snarls when I go to pet him. If he's on the bed with my husband and I go to get in bed he becomes very upset. It started with just me but he has been getting this way with my husband also. Im not sure what has changed other than my dog has become more cuddly with me and the fact that Im pregnant. So does anyone have a clue whats going on!?