Since i have become pregnant my dog is aggressive

Hi has anyone experienced their dog becoming aggressive when they where pregnant? My 4 yearold wanted to lay by me on.the couch and my dog was on the floor below me and all the sudden my dog tried to attack my son. Grazed his hand. This is the second time now he has shown aggression toward my son when.he never was like this before. Im afraid for my kids being bit and i also dont want to give my dog up but hes almost giving me no choice unless i can.figure out whats going on.