You feel better being off the meds because they did what they were suppose to do. They got rid of your anxiety and depression and you are now back to feeling "normal." Even if a medication helps you, it has some side effects, (like the weight gain from Paxil) and benzos and ADs are notorious for them Now that they are completely out of your system and whatever side effects they had on you are gone, it's very common to be amazed at how good you feel.
This intense tiredness you're feeling, which began AFTER you withdrew from the meds, COULD be a sort of rebound from the sedative effects of both Paxil and Vistaril. You took these meds for over two years and for that entire time you're brain was getting some help falling asleep and staying asleep. But that's gone now. Your brain is having to relearn how to get itself to sleep, which can take quite some time for a lot of people.
Even if you and your wife were thrilled about having your first child, there is a great deal of stress that comes along with that wonderful news. Most of the time we aren't even aware we're stressing about baby stuff, like how can we afford a baby, what if I drop it on it's head, what if the dog hates it, I'm exhausted NOW, how will I ever get any rest with a crying baby.......all that kind of stuff is floating around in our brains and in 9 months, it can really grind you down.
I'm not a doctor. (duh!) and my very best advice is for you to see the doctor who prescribed those meds for you and discuss what is going on. There may be some validity in my theory, but you should be checked out medically for a possible organic cause of your tiredness. Make sure you get your thyroid checked.........it is too often overlooked in young people and especially young men. There are a great many reasons you could be feeling this way which is why you need a good vetting.
Don't know if you've looked around lately, but about 10 out of 10 people these days list being overly tired as their number one health concern.
I, personally, haven't slept for about 7 years.
You'll be fine and congrats on the rug rat.