Suggest Treatment For Painful Black Spots Below Knee

Hi, My son`s age is 12 yrs. His platelet count was very low when he was at the age of 2 yrs. Sisil Rose of your hospital had treated him .After the treatment, the count was normal. since from a month , he has black spots (size - approx -25 paise coin)below the knee, which appears lilke blood clot. Gradually it disapears within 3 days and appears in another area under the knee only. He has a little pain when he touches it. what is it due to? should I consult the Haemotologist? kindly answer ..