Totally understand, and it's hard for a 3 yo to understand they need to wait while Mum tends to the baby when previously they had your full attention.
Try to have some time just with them, even if a family member can come over and tend to they baby a bit while you give the 3yo some attention, it all helps.
Also try to get them to help u with the baby, involve them as much as possible.
It does get easier, I promise