I'm at my wits end

Help me I seriously think I'm going crazy! 😭😭 I'm currently 10 w pregnant this pregnancy has taken a toll on me ! I have a 5 yo and an 18 month old! My 5 yo is amazing he's really independent doesn't need to be under me 24/7  my 18 month old on the other hand is the complete opposite! Which is crazy because prior to pregnancy he would come near me unless he was sick or hurt himself and his dad wasn't around! He's a daddy's boy! But now it's like he cries all day every day and that's not exaggerating! There's maybe 2 hours where he doesn't cry from the time he wakes up at 7am until the time he goes to bed at 8:45pm! And I only get that two hour break of pure silence if he decides to take a nap! Which rarely happens! But he cries and I have no idea why! If I tell him to go play with his brother or toys he throws himself on the floor and cries. Everytime I talk or look at him he cries. Nothing makes him stop. He'll have a moment we're he'll play with a toy and 5 minutes later he's crying again! I don't know what to do! It'd driving me crazy! And it's been going on since feb 5th! And nothing my SO or I do helps. We've even tried holding him but he'll just cry throw himself back and hit you until you put him down. We've tried explaining (as much as you can to a 18month old) what we mean when we tell him to go play or go get his cup! We've tried letting him just cry but it gives me crazy migraines to the point I feel like I'm going to throw up! Yesterday I let him cry and he didn't stop until he cried himself to sleep and my oldest came down "mommy why does he cry so much? He's making my ears and brain hurt!" And I feel so bad! I feel like a horrible mother because I've never been throwbyhis I don't know what else to do! Please someone give me advice because I'm legit going batshit crazy. 😭😭😭😭😭