I have just joined the gym and it has been a month since I have started the gym. I have done cardio for 3 weeks and 1 week body building but the problem is that while doing cardio I used to get tired little early and wasn't able to do little hardcore cardio.
For example: I couldn't do plank continuously for 1 minute.
So my coach told me that I don't have stamina and I should start taking protein or prework out which will help me in my workout.
Now I have started doing body building and my coach ask me to do 20 - 25 reps in each of my sets like biceps, shoulder, chest etc and so what happens is while doing 3 sets, in 2nd or 3rd rep I do some 10 -15 repetitions so my coach is telling me to take protein powder but I have a concern that using protein powder have some negative effects on body and when I will quit gym, I will lose all my pumping.
What to do?