Silly girl! Weight loss doesn't make you impervious to self-doubt!
You're a woman, you're single, you're young - did losing weight change any of that? Heck no! Look at any celebrity rag and you'll find an amazing, seemingly perfect woman talk about how she's filled with doubt when confronted with the opposite sex (or worse, being naked in front of the opposite sex).
Here's where you may draw your strength: everyone else is going through the same thing - no matter their body size, brain size or personality. Embrace your success. Embrace your new size.
When all else fails? Fake it. I have always been obese. I don't think I've ever had a lack of a date.

Not because I've got some spring of self-confidence that no one else has - ha! It's a matter of faking it. Swallow your fear and ask a new friend out to dinner. For me, the hardest part is the first step. You'll get the hang of it. I promise!