How can you gain muscle fast?
The fastest way to gain muscle is to first take a break from all your latest weight lifting workouts. If you haven't been lifting weights, you can start now.
You first want to let your muscles become de-conditioned to any weight training stimulus and let them fully recover from all of the other workouts you have been doing.
Then, start a full body workout program every other day or 3 days per week with a day of rest between each workout and 2 days of rest after the last workout of the week.
You should start out with very light weights and low reps. Then, increase the weight each workout and increase the reps until you reach 20 reps. Then, max out on 20 reps over the course of a couple of weeks as you raise the weight to a maximum for the final 20 rep workout.
Then decrease the reps to 15 and continue increasing the weight over a couple weeks of workouts. Then decrease to 10 reps using the same pattern. Then decrease to 5 reps while increasing the weight. Then go down to 3 reps and continue increasing the weight.
Over the course of the weight lifting program, you will have increased the amount of weight you are lifting by large amounts. This is what builds muscle.
You also need to choose the best weight lifting exercises in order to gain muscle fast.
And finally, you need to eat plenty of healthy foods and no junk food to ensure you are providing your body with all the building blocks it needs to build lean muscle mass. You don't want to gain body fat.
Try eating 500 more calories per day than the amount that keeps your body weight the same. This will slowly add lean muscle mass if you're adding calories from healthy foods.
Continue adding food as needed to continue the muscle gain over the course of the weight lifting program. You should be able to build 1 to 2 pounds of lean muscle per week. 2 is going to be difficult without adding body fat and too many calories. I would stick close to 1 pound of muscle per week.
Over the course of the next 3 months, you should be able to add 10 to 15 pounds of lean muscle mass. As you get closer and closer to your genetic potential, yes, muscle gains will slow down but you will look absolutely amazing already.