Its really hard hey hun. wiht him being up every 3 to 4 hours that sounds really normal for his age.
Have you tried a sling or carrier? that way he can be close to you and sleep and you can still do things wiht your 2yr old? Maybe he needs more feeds? Also maybe try co sleeping...thats how I get my sleep or i would be a mess

He is still so little and you wont spoil him with cuddles. Just remember this too will pass and your doing a wonderful job xxx