Yeah, I get like this. Sometimes you just feel ERKY. I usually pull myself out of it by pampering myself, having long, luxurious baths with a good book and glass of champers, putting a mask on, hair treatment, getting new undies or new anything for that matter. New perfume helps too!
Go out, not with the intention of finding someone (when you're looking, you never find anyone), just with the intention of having a fab time and tell yourself you look hot. If someone chats you up, then great ! ego boost! If not, stuff it, you're out on the town and can do WHATEVER you want to!
I felt like you about 2 months ago. I'd moved abroad, knew no=one, hated my flatmates. I did the above, stayed in and watched a heap of soppy movies and realised that I was being boring, in a rut etc, went out on a school night (yeah, ok, a work night) wearing dress I hadn't worn in years and got chatted up by a 20 yr old hottie which made me feel soo good, and my confidence went from there.
It will come back, breaking up is a ****.