Sorry to hear about your difficulties. I can't speak on the issue of the rash, maybe others can comment.
On the dizziness issue, I had most of my dizziness episodes while on the levothyroxine and armour combo when I was over medicated. I had postulated that I was overmedicated and having an issue with the fillers etc in the levothyroxine. Now I see that it was simply a matter of being overmedicated - I think too much T4.
Yes, it is entirely possible to have a reaction on the day you take your meds. So, your dizziness may be caused by too much medication in your system.
On dizziness, I know a dr would go crazy listening to me but, I have had to be able to differentiate among the different forms of dizziness I have experienced.
The one most relevant to you, is a fairly profound dizziness characterized by a bit of motion sickness when moving the eyes...like when I lay down to watch the tv, I feel a bit sick and get waves of dizziness if I have to move my eyes too much during viewing. Also, I feel a weird "buzz" in my head. When I was overmedicated this summer (I have some descriptive posts related to it on this board), I was severely dizzy, losing my balance and had major buzzing.The dizziness was such that my vision would vibrated and then move from right to left light an old science fiction tv screen that one was trying to tune where the images moved from side to side rather than up and down. It was scary and weird.
Now, I am a bit over medicated since I reduced my antidepressant (this happened previously on two occasions, so I know there is a concrete relationship). This time, I felt only super fatigued (weird I am one of those who becomes fatigued from being overmedicated), dizzy, a bit nauseous and the faintest buzzing in my head, and a massive headache.
I was not sure at first, since the fatigue confused me - but one the vision problems, buzzing and headache started, I reduced me medication and it has passed.
The difficulty with dizziness is that it can also come from a number of other sources and here is where a dr would go crzay listening to my ability to differentiate among types....but here goes.
In addition to the overmedicated dizziness, some people, myself included were dizzy from being hypo, and thus undermedicated. Also, I have felt dizzy from the armour while I was adjusting to it. It is considered normal and nothing to worry about. But, each time I felt the dizziness, esp after upping my medicaiton 1/4 grain, I felt sort of good, like the dizziness one gets after a cocktail - though none of the other fun stuff.
I know you are scared. My bf was forever criticising me for making decisions about my medication and having varying blood levels of the thyroid hormones. I know it was probably not the best thing to do, but these are very powerful medications, and your body can react quite strongly to being overmedicated and you can't always wait for a dr to respond. I don't advocate DIY medication, but in some ccirucmstances I can understand how people do what they must.
I probably would act conservatively in switching back to the levo, if at all, because you don't know your blood levels after switching to armour (too much at 90 mg) and then to 45 for a couple of days. You may have been overmedicated on the levo to begin with. Believe me, you will not suffer as much from taking too little rather than taking too much.
Remember, the half life of t4 is one week, ( The half-life of a medication is the time it takes for your body to metabolize and excrete a drug so that half of the drug is removed from your body), so the meds stay in your body quite a long time. A medication decision you make a few days ago can still be influencing how you feel.
My final advice, be conservative with your medication, don't overreact - your body has plenty of hormone, and try to get in touch with your dr.