Hi Cristina,
I hope your health issues have improved and that you have some answers.
I thought I would add to the forum as I have also had a returning insect bite - in fact two - and I also got them in northern Italy - Genoa to be precise. I've had plenty of mosquito and tick bites in my life and these have been different. The first bite happened right after I arrived, I was bitten in the night and the bite lasted about four months, flaring up every couple of weeks or so as you had described. This one went away but I then got another one and it has been about eight months now (intense itching unlike a regular bite that can occasionally last for about an hour - however the bite site itself doesn't look like much, just a small bump). I recently itched it so much that it formed a scab which I thought was probably a good thing because I figured I could squeeze the thing and coax out whatever might have been stuck in there irritating it. That was about a week or so ago. Of course I'm slightly concerned about your autoimmune problems and would like to avoid anything similar. However, I wonder if they might not be related. At this point, the bite is oozing every few days and I give it a squeeze (eww - sorry about the graphic details) it's certainly improved. I'm wondering why no doctor sought to open up your bite and drain it.
Anna