You're 5-10 123 male and you think you might be a bit skinny?
Is there a typo somewhere?
I'm not in the 'bulk up to 200 or you're a pussy' crowd but DAMN!
Setting goals of gaining 14 pounds of muscle and having a 6 pack for the same program is guarantying failure.
Gain the weight with some fat then lean back down. At your height-weight some fat may be GOOD for you.
You can do it with bw training but I'll leave the local experts to help you with that.
Sweat is fine as long as you don't dehydrate or get into heat stress.
Cold showers probably technically do burn a few calories but not enough to bother doing it. You need to gain weight anyway.
Just eat a lot of healthy food and probably drink a lot of whole milk.
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