Any suggestions?

This is very long so I'm grateful if you read it all.

I've tried all I can think of. My baby is 15 weeks old and she only sleeps half an hour at a time in the day she will be awake for about an hour-2hrs then have a 30 min nap and this goes on all day after about 1hr of being awake shes so mardy because shes overtired but whatever I do she doesnt want to go to sleep shes awake for another hour nearly and I have a toddler so I cant spend ages trying to get her to sleep I try then after about 10-15 mins I have to give up and try again later as my toddler needs me. I've tried getting to her just before the 30 mins had passed to try help her into another sleep cycle but that doesnt work I've tried sleeping her in her crib upstairs but she wont settle on me and she won't settle by herself so at the moment its pram naps. I put her in and rock her to sleep. Then if she stirs I have to stop whatever I'm doing and stand and rock the pram and I have to rock her initially for about 10 mins before she drifts off enough for me to stop or else her eyes ping open and then shes awake for another hr+. But on a night time its different. She has her last bottle around 7pm and falls asleep within around 10-15 mins on me but in the day hates me trying to get her to sleep on me. I then put her down in her crib and she will sleep for about 4-5hours and I can normally settle her with her dummy after about an hour sometimes less shes stirring again and just cant settle herself. She doesnt wake up she just whines and fusses. I try rocking her back to sleep and it works sometimes but only for another hr or so so sometimes I have to feed her but shes not taking a full feed maybe only 3-4oz whereas shes on 7-8oz 4x a day so shes getting enough milk in the day I think shes just relying on it to drift back off. After a feed she will then sleep another 4-5 hours and around 5am shes stirring again but I dont really like feeding her as it's too close to her first feed of the day at 7am. If I feed her around 5am she doesnt take a full bottle at 7am then it messes up are day feeds so I'm not sure what to do. The only way to settle her from 5am is for her to sleep on me which then means I dont sleep. I've taken to feeding her when she first fusses around 11pm because then I know I can get a solid 4hrs. For me to get enough sleep to function I have to go to sleep just after shes in bed so I have to go to bed around 8/9pm wake to feed around 11/12 then sleep till 4/5am then I'm up. Most of the time I never go to bed that early because im busy doing everything I dont get chance to do in the day. But it's taking a toll on my relationship as he doesnt get in from work till around 7pm just after ive done bedtime then I sort out bottles, laundry etc then go to bed so we dont spend hardly anytime together and all we do is argue about spending time together. He doesnt wake to sort her because he works long hours so he sleeps and sometimes not even in our bed and neither of us know how to encourage her better sleep habits. Our first daughter slept through from 10 weeks 7-7 so this is very different for us. I'm tempted to put her in her own room already because maybe we are disturbing her I'm not sure or because our bedroom is in the front maybe cars etc are disturbing her but we dont hear them because we are used to sleeping through it. I dont know what to do and I dont have any help because every family member refuses to look after her because she cries to much and is hard work so I cant rely on anyone for a break and my partner works 12hr shifts with about 3-4 days off a month so hes not around enough to rely on for help or a break, or even to catch up on sleep. No one can give me advice then health professionals have just said ride it out but I cant carry on like this I cant function in the day I cant keep my eyes open most of the time and with a toddler who needs me too along with a baby that cries most of the day but refuses to sleep my days are long and hard. I'm doing as much research as I can and getting as much advice as I can to sort her naps out the night time will improve as she gets older i hope but she needs the longer naps more for her than for me shes not a happy baby sleeping 30mins at a time.