It sounds like the mirt is pooping out on you, also known as tolerance withdrawal. Taking more would't be advised because mvwaugh noted, less is supposed to be more helpful for sleep, and likewise, more can mess up sleep. I'm not sure what to say about the peeing, since that has not been an issue for me. I did have one night, though, where I woke up and HAD to go, not normal for me! I have also had the rare chest vibration you mentioned. I am in the process of tapering mirt, so it is interesting that I had that as a WD symptom while you had it while taking your same dose, perhaps another indiction of tolerance withdrawal.
At any rate, is it still helping you with the original reason for gong on it (depression?)?
Why is it that you can't take SSRIs? What problems did you run into?
I was on Effexor, went off too fast last year and was eventually put on mirt because I couldn't sleep or eat, but it pooped out on me very quickly at 37.5 mg, so my doc reinstated the Effexor and within an hour I felt dramatically better, a sure sign of dependency! Combining mirt with Effexor is known as California Rocket Fuel in the psych profession, and supposedly the two together work better than each by itself. My goal is to taper off both because I have been on ADs for nearly 20 years want to be done with them and deal with my emotional issues in a non-drug way. The drugs simply muted my emotions and kept me from feeling, but tolerance allowed the original issues to persist, since drugs never fix those.
So, if you decide to go off mirt, spend some time in the mirt withdrawal section on this site. It is NOT a pleasant one to get off of and you would be advised to do a very slow taper, ideally 10% reductions every 3-4 weeks. Otherwise, withdrawal causes so much suffering that people end up reinstating. You may find that on a lower dose your sleep will get better since it is more sedating at the lower dose. If you taper too fast, though, sleep can be greatly impacted.
If you are able to tolerate an SNRI, it could be added to the mirt since they seem to do well together. However, your system may be getting sensitized to where you can't tolerate any of it and have more side effects that are unacceptable. People in this bind end up polydrugged, since docs don't seem to understand that withdrawal symptoms can be the same as the condition the drugs were to treat originally, and so they chase the symptoms with more drugs. Each drug causes its own side effects which the doc then chases with yet another drug. So, beware! You do NOT want to go down that road!
You could try Benedryl to aid sleep. I have had good luck with taking a magnesium glycinate supplement, which helps anxiety and is calming. Drinking milk at bedtime can help as well, though won't improve the pee'ing problem. In general, I would try to cut drinking anything after perhaps 8 pm.
Try taking mirt earlier in the evening on the days you don't have to drive to see how sedating it really is. It may be that you could stay alert enough to drive even though taking it earlier.