hello.
thanks for posting your query.
i hope you have not been picking up on any of the lesions as that will lead to deep scars and pigmentation.
you need to follow a routine of cleansing, sunscreen , creams daily.

cleanse your face with cetaphil cleansing lotion for acne prone skin thrice daily.

sunscreen needs to be used daily , neutrogena would be a good choice.

creams would be:-

clindamycin gel on the active acne lesions in the morning and Retin A 0.025% cream at night on the entire face.

Retin A needs to be applied only at night, start with coming it for 2 hours and then gradually increase the time interval to keep it overnight.

this will take care of pimples and marks.

for dandruff you can use ciclopirox oleamine shampoo twice a week. grey hair have no treatment. you can take calcium pantothenate supplements, but it may not be very helpful.

please let me know if you have any queries.

Hi welcome to Health care magic forum. Pimples are a universal problem, you didn't mention your age if still in teen age it might be genetic. try to find out whether any one in your family have gray hair in small age. Causes of gray hair in others is malnutrition , anemia, mental stress.
It appears that the gel you have used didn't suit you. it is allergic to you, causing and caused allergic reaction like itching and dandruf. So i advise you to discontinue the gel .
I advise you to consult a cosmetic dermatologist or a trichology clinic for diagnosis of the internal problem, and treatment.
Besides i advise you some diet recommendations as Take more of green leafy vegetables, pulses, sprouts, egg, chicken, meat, milk, fruits, juices, and dry fruits. Which increases blood, general health, resistance of body to such things, and stamina to lead comfartable life.
Also try to follow some diversion procedures as yoga, meditation, reading books, and hearing music, which reduce the mental tensions. Wishing for a quick recovery and thanks for calling.