How can I change if I have no motivation?

Lately iv become really depressed, well lets say for many years, but this yr I would have to say this is the peak of it. I will tell u straight off, i guess asking on yahoo is a risk cos of possible bad comments but here it goes. I am saddened due to the fact that I lack social abilites. I dont have a disorder but im fairly quiet. It seems that boistorous people are overwhelming to me so I dont relate to them. Also I have vibes that some dont want to approach me or talk, even those who are the confident type. I do have some good friends but I want to meet new ppl, I just feel so out of place. I have also had problems with girls, they just dont seem interested. If i were to approach a girl (very rare) it would be subtle and simple talk, I dont come across as bad, or ugly. But at the end of that small convo it has not reached my fulfillment. I re yse as well how I appeared to that person. I am 21 by the way and very lost. How can I change?