It sounds like everyone is having a hard time adjusting to the new situation mummab.
Please keep in mind that what is best for you is also best for both your boys so while your older one is adjusting to sharing you & learning what the new boundaries are he will get there & it sounds like you really need them for your own peace of mind.
I wish I could wave a magic wand for you to stop time so you could get some sleep.
Sending you lot's of hugs & hoping both the sleep & reflux settles soon...
Have you thought about cleaner or someone who can help watch your older boy for a few hours while you rest with ds2?