More sympathitic, I could not be. I have suffered from this affliction now for more than 25 years. The purple spots are most likely bruising caused by the frenetic itching. The problem you will have when being seen by a doctor is that there will be no evidence of a skin disorder, just the damage you are doing by scratching.
There is nothing over the counter that will help with the itch, and most likely moisturizers will just make it worse. It isn't a dry skin problem,.
One thing that will help a little is to get some aloe, (in a gel form is best), and keep in in your freezer. The more you scratch, the more sensitive your skin will become, and the icy cold aloe will help with that aspect, though will do almost nothing for the itch.
This is one of the most frustrating things because dermatologists will tell you to use some colloidal oatmeal, or take some benadryl. It is impossible to make them understand how life altering this problem is. I have gone weeks without a decent nights sleep, or drugged myself sufficiently to get a little sleep, only to find myself dysfunctional the next day. I have gone so far as to use sandpaper on the itching, and then once it started to bleed, (my skin bleeds almost constatntly because of all the scratching), i poured gasoline on it. The sting and pain it caused was preferable to the itch.
I don't recommend this howvever.
Two things I have found give some relief. First, ice, or ice packs. If you cover the itchy areas with ice packs, (the flexible ones are best), it will generally settle the itch down long enough to get a couple of hours sleep at nightl. I have started to keep a cooler packed with these next to my bed, so that when the effectiveness of one wears off, i just grab another. Yes, it's cold, but it's better than itching. I also have a swimimng pool in my backyard, and when it's cold like it is now, I find that taking a swim before bed helps also. I use ace bandages to hold the ice packs in place while I sleep.
Second, I found a doctor that diagnosed the problem as neuropathic, which would explain why there is generally no real rash or visible defect on the skin itself. He prescirbed neurontin for it, which I take every day. At first its a bit of a knockout punch, but I have found over the years that with the medication, the bouts are less frequent, and a little more controlable.
sorry for the long answer, and I wish I had an easy answer for you. I hope for your sake it's temporary, and just goes away.
Good luck