Okay, I read 21 months not weeks....She's still very little. At five months they are going to wake-up hungry...their little tummies are so small and they aren't eating solids yet. The below advice is for a child that is already eating solids....I totally read months and not weeks.
Just set up a routine in which you make a feeding as quick and painless as possible. Because five months is an iffy time...they may or may not sleep all night. I had one that did and two that didn't. It will be over before you know it.
1.) don't turn on lights....just feed her in the dark with a night light.
2.) Don't talk...no stimulation. Just feed her, burp her, and then lay her back down. (I won't even change a diaper unless they are really soaked....I would rather change sheets than wake a child up and then spend the next hour or two of precious sleep time trying to get them back to sleep.)
And it's just normal for a baby that age to sometimes need a feeding. One is not bad and if you just feed her, burp her and lay her down...you are training her to go back to sleep quickly and she will stop waking. My son is 14 months now. He's been getting up once up until I had to cut him off recently. I could have probably done it around nine months or so, but it was no big deal to me to just feed him quickly one time during the night.
Maybe you can keep the below advice in mind for when she's eating solids.
Seriously she's not hungry per se. And she certainly is not going to starve to death. My son has been cut off now from breast feeding because my youngest daughter came home with lice and I had to treat everyone...including myself...so no more breast feeding (I can't pump). I thought he would be a beast in the middle of the night and so dreaded it.
But I go in put the pacifier in his mouth, pat his bottom and tell him it's night-night time. He cries for about a minute and goes back to sleep. three times now in the last week he's slept all night.
You need sleep and she needs sleep. She will stop waking if you make sure she has no reason to wake up. Make sure she has a snack before bedtime or a good bit of milk....brush her little teeth so she doesn't have milk sitting on them all night causing cavities...and the put her down. She will sleep all night after a few days. Most don't take long to realize that no one is going to pick me up and give me a bottle. My oldest took three nights and each night got easier until she just slept.
1.) Don't give in or she will just cry harder until you give in.
2.) Don't pick her up....just gently lay her back down and pat her little bottom....maybe sing to her softly and tell her it's night-night time...time to go to sleep.
3.) Check on her every 20 minutes or so and go through above routine again until she gives up and goes to sleep.
Three to four days max...you might be lucky and she gets it the first night????
Good luck!!
PS I see many saying that each baby is different and you have to listen to their needs...to some extent that is true, but I disagree with letting a little one dictate what they will and won't do...
She's more than old enough to sleep all night. And even if she does wake up for some reason, you just insist that it's night-night time, lay her back down and kiss her and leave. Even my six year old will wake up from time to time. I check on her, tell her it's okay, kiss her/say I love you, and leave. She goes back to sleep.
You have to train her....not let her train you. What a horrible thing to do to a child....you spend the first year, two years, three years???? letting them know that you are at their beck and call, submitting to their every whim and demand and then at what age 4 or 5 they have to listen to you and follow your advice and instruction????? That's silly. You start out from the beginning training them for what they need to do...gently, with love and understanding, but with insistence that you are the parent and they will learn what you are trying to teach them.
Please