Originally Answered: Is sweating good if one wants to gain weight and gain body mass?
Sweating is perfectly normal for everybody. It's one of your body's natural mechanism of eliminating excess salt and some toxins. Just be sure that you replace the water lost by sweat by drinking 3-4 litres of pure water each day (coffee, tea, soda, juice, or anything at all that has flavour or colour don't count). Always have a water bottle with you and discipline yourself to take sips every half hour or so.
If you want to gain weight, then consume complex carbohydrates a little bit more generously (don't overdo it though), protein, and vitamin B Complex. And get a trainer to show you what workout routines are best for you. (You seem to have that already, eh?)
Complex carbohydrates: carbs that are attached to some fibre- and vitamin-rich elements, e.g. fruit, wholegrain bread/flour, brown rice, rye bread, oatmeal, corn, fresh pasta made from wholemeal, potato with skin (not fried). The opposite of complex carbohydrate is processed or "white" carbohydrates, which you should avoid, e.g. white rice, glucose, dry pasta, instant noodles, white bread, sugar, french fries, potato without skin. Complex carbs are recognised by your insulin and absorbed to nourish your cells, therefore giving you energy. White carbs are rejected by your insulin, fails to feed your cells, get stored up as fats, and are prone to be oxidised by free radicals to create long-term problems like cancer and heart disease. I know your objective is to gain weight, but certainly you don't want to be always tired, shapeless, flabby, and full of toxins. So in any case, stick to complex carbs.
Protein: these are the main ingredients for your muscle. Your best protein source is animal protein, especially fatty deep-sea fish (salmon is the best, tuna is good too) and fresh cow's milk. Other good sources for protein are chicken/white meat, eggs, legumes, yogurt, and soya. Eat 3-5 servings of protein per day, 1 serving being equal to meat or tofu about the size of your fist. If you want to learn how to use protein to your body's maximum advantage, the best thing to do is a Jewish person about a kosher eating pattern; or at least a Muslim about hallal.
Fat: good fats come from deep sea fish, extra virgin olive oil, avocado, and fresh milk. Dark semi-sweet chocolate is good for you as long as you don't overdo it (no, I'm not talking about Kit Kat or Snickers... or some sugary a la creme from Godiva). Avoid fats from fried food, processed food, and meat fat/skin. Good fats feed your cells, enhance your muscles, and takes care of your organs. Bad fats make you flabby and drains your energy.
Eat 6 times a day: 3 meals and 3 snacks.
-Breakfast: be generous on complex carbs and protein, have 2 servings of fruit
-Morning snack: protein, fruit, and a bit of carb if you like. drink milk.
-Lunch: a reasonable amount of complex carbs and protein (not as much as morning), fruits and vegetable in abundance.
-Afternoon snack: same as morning snack. milk.
-Dinner: same as lunch, but halve the quantity.
-Before bed: no carbs. protein and fruit. milk.
So no, don't worry about sweating. Just adjust your eating pattern to the above and you will be completely fine.