What Causes Small Tiny Red Dots To Form On The Legs?

I'm 12, from Singapore. Basically, I've been to the doctor for my sickness, but I forgot what it's called. So if you could tell me what it's called, I would be very glad. I have had this sickness basically twice. And this is what I basically came up with - 4 stages. Stage 1 - small little tiny red dots form on my legs. Yes, only my legs. Stage 2 - the red dots become more, yet still only on legs. Stage 3 - the red dots fade away (even without medicine, it still fades away). Stage 4 - the red dots reappear, this time around 10 times as big as Stage 1 and 2. The previous time I got this sickness, I had to go to 4 doctors in total. First, I consulted some random doctor who simply gave me some cream to apply and medicine to take if it itches. When it still didn't fade, I consulted my family doctor who referred me to the polyclinic (government clinic), claiming he did not know what sickness this is. When I went to the polyclinic, the doctor there still did not know what sickness this is, and referred me to a hospital, to the special skin specialist center. The junior doctors there did not know what sickness this is, and I was referred to a senior doctor. He said it was some ha-i'mnotsurewhat disease. He said that this sickness is not uncommon, but might affect the kidneys. Therefore, I took a blood test and a urine test, together with a skin biopsy. And after all that, strangely, without any other medicine (yes, the hospital did not give me any medicine) for my legs, the red dots faded away. Now, I have a relapse and I'm going to the hospital pretty soon again. But the main point is I would like to know the name of this sickness if you know of it.