How do i get over my anti-social ness?

I'm very anti-social and shy, i dont talk alot, i was like this all through high school, i only really had like 2 bestfriends, i talked alot around them, but when it comes to new ppl im soo self conscious, i worry a great deal about what other ppl think of me ( or what there thinking) it has really held me back in life, it has hurt my relationships with men, I dont no whats wrong with me, its if somebody talk's to i just think there looking at my flaw's or judging me. idk why i cant just be normal, and just not care what ppl think, im thinkin about joining the navy also, so i would like to make friends while im there, i dont want to be the girl that's all alone, cause she scared of ppl, idk i wouldnt say im scared of ppl, cause ive been on dates where i talk for hours, but i guess freeze up at times, it take's me awhile to warm up to ppl, How can be more confident and social?