MK-677 will not affect sex drive in any way whatsoever. However, right now you need to look at why you might be stumped for results. At 19 you should be getting the best gains of your life. What does your diet consist of? The absolute biggest key to results is diet and it's at least 80% of it if not more. Training needs to be right as well. Before looking at something to enhance your performance you should be looking at where your problems might be.
Check out this thread on diet and nutrition to give you an idea on what you should be doing
https://www.isarms.com/forums/steroids-sarms-information/diet-nutrition-basics-101-a-3314.html
(PM me for a price list for Biotech Labs and 10% discount)