I am 27 and I have been underweight for many years. Recently, I began to have consistent training sessions in a nearby gym. My personal trainer advise me to buy several supplements. They include whey protein, glutamine, creatine and amino acid.

I would like to know:

1. if there are any side effect
2. the dosage of these supplements
3. whether I should take them daily or pre/post-workout
4. whether I should take them for a month then stop for 2 weeks, or just keep taking them as long as I have regular training like 2-3 times per week