H.,
You know, I feel like my daughter did the same thing around that age. She's just turned 1, and has been sleeping great for quite awhile now, and she started sleeping through the night at 6 weeks old. Then around 7 or 8 months she was up screaming all the time. I understand how awful it can be... for the fact that you're not sleeping and also because you worry so much about what's wrong. With Emma, I think it really did have a lot to do with teething. She had about 6 come in at one time and one right after the other, but I feel like it took months for them to actually come in! She just had teething symptoms forever, poor baby! But you also might want to keep an eye on her ears. Emma's only had 2 ear infections, one when she was 7 months, and then another a couple weeks ago. Both times, whenever we laid her down, she screamed. But this was when the ear infection was pretty bad. She could have a lot of pressure in her ear where it hurts to lay down, but she's not really showing any other symptoms. With her last ear infection, we were at her 12-month appointment and the doctor told us she had an ear infection and we were shocked! She hadn't been acting any different! But 2 days later, there it was. She had 102 fever WITH motrin, and just laid on my chest and moaned. It was the worst thing ever. I couldn't ever lay her down in her bed so I slept upright with her on my chest in her rocker all night. Anyway... I got on a rant, there, I just wanted to encourage you that there might actually be a reason your little one isn't sleeping. And if there's a reason, then there's a way to fix it. And also be assured that it DOES get better! Emma's a super-star sleeper. She definitely has her moments (or nights), but she's great.
Good luck!
-S.