When does it get easier?

I am 12 days PP and absolutely in love with my litte one. I am really struggling though with the lack of sleep. She has been up every 30 minutes to 1.5 hours constantly (to eat) for the past 10 days. We found out a few days ago that she wasn't gaining weight so we have started to supplement with formula for every other feed. She still isn't sleeping much longer then before...maybe we aren't offering her enough formula. She was up every 20-30 minutes from 11:30pm-4:30am last night. It was miserable! I couldn't figure out why she was so fussy and refusing to sleep.

I just want a little sleep...2 hours straight would be great! When did your little ones start sleeping for longer periods of time?