Can I get some advice on my sadness?

Im not suicidal at all or anything. I just go from moments of thinking "my life is decent" I have a job a car that im trying to rebuild but still I hit lows of sadness and loneliness. For example yesterday I was fine but today I just felt this incredible loneliness.. i've always been a sheltered child. My parents aren't social AT ALL. So I never picked up the social skills I need to make and keep friends. I have like a total of 3 friends. Im 23 and ive only had 1 gf who left me like 6 months ago because I was boring her with my lack of ability to talk to anyone or make friends it was just me and her daily so she got bored. So now I have no friends from high school no friends really at all. So I suffer from severe loneliness when I have free time. I feel like im forcing myself to be happy. I can say im happy because I ALWAYS TRY AND KEEP AN OPTIMISTIC ATTITUDE and sometimes I am but sometimes I just don't feel happy. Am I depressed or something? Because sometimes the sadness gets overwhelming..