Urticaria pigmentosa is usually seen since childhood. As You are getting this since 4-5 years, I suggest you to take a second opinion and get it diagnosed. You can post photographs also to get it diagnosed. In any case, if this is the disease, it generally has no permanent cure. Homoeopathic medicines can help you to control it.
Apis mel 30 is an effective medicine for treating urticaria. The 200 potency (power) is high, so the high potency may cause an aggravation (worsening of symptoms). So it is safe to take Apis in 30 potency.
Urtica urens 30 is also beneficial in treating the symptoms of Urticaria Pigmentosa.
Yes homoeopathy can be helpful in your case but if apis hasn't worked you need a proper medicine according to your body type as apis might be acting too superficial being a specific remedy consult and take 2nd opinion
Urticaria pigmentosa is also known as Mastocytosis or Mastocytoma. If you are confirm in your diagnosis then take proper treatment . It should not be treated like simple urticaria. It is a generalised systemic immune mediated disorder requires careful management .Take care.