G.M.
start feeding her breakfast and dinner with either rice or oatmeal cereal, or both. she probably is hungry! at 5 months she needs to eat, especially since she is at the bottom of the chart for weight. Also increase the amount of times you breastfeed her in the day...NOT THE NIGHT! You will cause her to get used to waking up at night to feed, then you'll be sleepless for a long time. Feed her in the DAY.
also buy this program...sleep sense program by Dana Obleman. It changed my families life in a matter of days!! It took over a month for my son to completely do what she says easily, but seriously within days we were all functioning better and sleeping! And he wasn't waking up to feed at night. Well worth the 50 or 60 bucks we paid. (can't remember now)