Jealousy

So unfortunately I have always had an issue with jealousy. I have caught my bf a few times checking other girls out and it makes me so mad. I have argued and he says he can't help it. For me, ever since we have been dating I honestly don't find any other man attractive. idk why I just don't. Ever since I found out I was pregnant it bothers me even more and even if he isn't doing it I feel like his is... Is this a normal thing or just me!??