The blotchy discoloration can be due to hyperpigmentation skin which is darkening that occurs when an excess of melanin, the brown pigment that produces normal skin color, forms deposits in the skin.
Treatment involves hydroquinone, azelaic acid, corticosteroids, tretinoin cream and laser treatment. Please discuss these options with your dermatologist before using them.
Regarding the bumps on the birthmark, it is best to get it evaluated from a dermatologist as any change in a birth mark or mole should be evaluated from a doctor.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.