Arguing UPDATE

Hubby and I have been arguing so much more since we found out I'm pregnant after trying for 5 months. I don't understand it. I know there's a lot of new stuff going on, but it all makes me feel even more committed and in love with him and so excited for this journey. But we argue about every other day now, big ones that ruin the night. And the more we do, the more I get the sense that he's not as into this marriage and family as I am. When we're not arguing he disputes that when I bring it up. But I can't shake the feeling. We're also arguing right now, though I literally have no idea why or what about.... I just want all this to stop. I love my husband and our little family. I'm feeling so defeated and broken right now. 
UPDATE: Despite me being at work long before he woke up, he's now saying he doesn't think the baby is his, he's gonna leave us if I can't prove that it is, etc etc. Yesterday around 7pm he was telling me how excited he was to go to the first ultrasound and hear his first child's heartbeat and he'd do anything to make sure he's there.. Now this. I'm trying to stay calm for baby's sake, but how the hell am I supposed to handle this?! I think he's just being an ass and doesn't truly mean it all, but that thought doesn't really help me right now.