Oh, you poor thing! I definitely feel your pain.
I couldn't tell from your original or follow-up post whether you're going to be seeing a specialist, but I really recommend it. You are really suffering right now, and it is time to get to the bottom of this.
I think a sleep study and a sleep specialist would be a good first step, but a psychiatrist may also be helpful, as well, because they know all the best meds and stuff for sleeping and for anxiety.
I do have a few specific thoughts of things you could look into. First, have you ever been prescribed Trazodone? It is a very common med for folks who have trouble sleeping and take any other depression/anxiety meds. It's actually an old, very safe, mild, antidepressant that they don't use much for depression 'cuz it makes people soooo sleepy!!
There is a wide range of dosing possibilities on trazadone, from a tiny dose that is only a fraction of the amount a person would take for depression to a massive dose that will practically put you in a coma. I hate the stuff, but I've gotta tell you that if you take enough of it, it WILL put you to sleep. Now, that being said, you'll feel pretty fuzzy and "hungover" the next day, but in your situation with your insomnia being so, so bad, it might be better than how you normally feel! Trazodone is great because it is non habit forming, completely safe, and you can take it as much as you want. It's super, super unpleasant, I've gotta say, but it really does work. You are so bad off right now that something like this might really offer relief.
Second, I have had a lot of luck over the years with regular old benadryl. Others scoff, but whatever
. I very occasionally take a DOUBLE dose of ordinary benadryl and it tends to work pretty well with just a tiny bit of "hungover" feeling the next day. I know you mentioned benadryl, but you may want to ask your doc if you can try a LARGE dose of the stuff. Again, like trazodone, benadryl is great because it is a very safe medication.
Third, I'm wondering about your Xanax that you're taking. Do you take any other psych type meds? The reason I'm asking is that benzos (that is what Xanax is) can over a long time cause all sorts of weird issues that basically come out of dependence/withdrawal. A lot of people (and their doctors) are unaware that benzos can play a role in things like INCREASING anxiety, insomnia, etc. I took Klonopin for a very long time (it's related to xanax). Although it was initially helpful to me, over time, it began to create a situaiton in which my body was constantly needing it or withdrawing from it. The result of withdrawal? Anxiety. Yup. My anti-anxiety med was actually causing cycles of anxiety. Doh!
So if you've been taking this same dose for a long time, it could be that you actually need a higher dose, because your body has become habituated to it, i.e., you're having breakthrough anxiety that is preventing you from sleeping. I'm also wondering if you may be experiencing some mild withdrawal symptoms at night, as well. If you're taking your xanax earlier in the day, then at night, the levels of the med in your blood are dropping, causing increased anxiety and jitteriness. Basically the fix for this would include a) going to a slightly higher dose and b) spacing your doses out appropriately.
You may need to put yourself on a schedule -- say, 1 mg of xanax every 6 hours or whatever. Right now, you're taking it as needed, which means your blood level of the med is jumping up and down unpredictably. This causes mood swings, anxiety, etc. A psychiatrist could help you figure out how to take xanax and also whether there is another benzo that would work better (a longer-acting one that you could take once or twice a day, maybe?
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Xanax is a great med for short term anxiety stuff, but very very bad for the long term. Everyone who takes it for a long time and at increasing doses eventually develops problems. A lot of doctors don't know this! A thought for you for the future would be shifting over to a good antidepressant that is approved for anxiety. Zoloft, paxil, and some other antidepressants are the first line treatment for anxiety, and will help a ton more than short-term fixes like xanax. But it's not something to worry about right this second, necessarily.
Anyway, sorry this was long. I hope something in this will be at least slightly helpful. Feel free to PM me any time! Insomnia is the absolute worst and it sounds like you're being pushed over the edge
I've got baby blues pretty but so I'm scared it might escalate to PPD. DH is worried and I plan to talk to my OB at my postpartum checkup next week but 
