(((hugs))) Boy, I can't count how many adoptive moms have BTDT. You are by no means alone!
Our first adopted child was 26 months old when he came to us, with no identified issues. WHAM!! Were we put through the wringer! I remember listening to him tantrum (he used to scream for an hour or two at a time) and crying just outside his door, trying to talk quietly to help him calm down. (Being in the room where he could see me would escalate his tantrum.) My bio child was a basket case, demanding that we 'send back' the newly adopted child. I thought we'd done the worst thing ever. How could we have thought this was a good idea?!
We finally, after two years, got a referal to a child therapist. The therapist gave us some tips and things to do, and then suggested ever-so-gently that we have our little one screened for FASD. (Fetal alcohol spectrum disorder, also known as FAS/FAE.)
We found more help along the way, working with various professionals.
But the point is that adopting a child from foster care is no bed of roses. I felt totally blindsided by the issues we faced. We were ready for a kid who was scared, and we'd attended all the classes and stuff...but THIS was totally out of our understanding. We learned, we're coping. It took time and that was something that I hadn't anticipated, either. Time.
I also had thought that I would be this wonderful loving mother. Oops. I wanted to be, and I was trying, but part of me was just aghast at what was going on in my home - my bio child was falling apart, my adopted child was a screaming, hysterical mess, and I was playing monkey in the middle. I felt overwhelmed and unsure how to handle this little kid who had so much rage and so many issues.
You might look into Early Intervention, if you haven't already. They can help identify any developmental lags and see if there are some underlying issues as well. We had an occupational therapist who helped us immensely. (A private OT, not through Early Intervention, but you might find one through your local Early Intervention.)
Once we figured out that our new child had dysfunction of sensory integration many things eased up for all of us. Turns out the poor kid perceived all touch as pain, so was always hypervigilent in case someone might touch him at all. Hugs from other kids were particularly traumatic. Made getting together with other families for play dates a hellish kind of bizarre.
But all of that took a couple of years to figure out and get a handle on. If I had it to do over I would ask for help sooner - but I didn't know who to ask, so I didn't. I'd also work to have specific alone time for me, for me and Dh, and for me with each child. This can sound overwhelming, but it doesn't have to be a long time for each. Even 15 minutes or half an hour can be a refreshing break. Maybe have Dh watch your new son while you go for a walk around the block with one of your Dd's. Then the next day, switch and take the other Dd. Or go for an ice cream cone (BRRR!) or hot chocolate. On the 3rd day get a babysitter for your girls and you and Dh take your Ds for a walk together. Then once a week (or as often as you can swing it!) get a babysitter and go out with Dh. Again, it doesn't have to be The Most Romantic Date Ever, only a little break. Just find something that is non-demanding, relatively calming, and that you could enjoy with each of your kids and your Dh.
I notice that you live in my state.
Feel free to PM me if you want.
Oh, and our oldest adoptive child is doing well now. We have adopted three more, and each has come along with their own set of issues. The family dynamic has had to stretch and grow, but it has happened. Eventually.
I tend to remember the first 2-4 months after a new child has joined the family as very exhausting, very trying, and generally Not Fun. (Which was unexpected, the first time. After that I knew better than to expect instant euphoria - but it still got me down.)