Try doing 3 sets 10-12 reps with a average to low weight. Ease yourself into a routine, dont just start lighting the heaviest weights possible straight away. Cant remember what I started with tbh. My metabolism used to be quite slow, but has picked up a decent amount over the past few months.
Try to work different muscles each day. Day 1- Shoulders, Day 2 - Back and Bis, Day 3- Triceps and Chest, Day 4 - Legs/ Cardio.
Also try to eat loads of protien eg Chicken, Eggs, Tuna, Beef, Turkey, Nuts and drink milk.