Any tips on combatting regression/ making a sleep schedule?

[SpotlessMind88]

This is my first baby, she is 4 months and 2 weeks. She has never been a great sleeper (unless she is in someone’s arms). The longest she has ever slept through the night in her cot is 3 glorious hours (this happened on two occasions). She hates her next2me crib but co-sleeping isn’t an option. Since she turned 4 months her sleep has gotten worse. Every time i put her in her crib she wakes either straight away or within 10 mins and cries until I pick her up. Sometimes she’ll have a little feed or just wants to be held.
I’ve read that now is the time to set a sleep schedule with 3 naps a day and a night routine that may involve putting her in her cot while still awake?! Does anyone have any tips from experience? I’m running on empty, I get to catch up on sleep at weekends when her dad takes her for a few hours in the morning.
FYI she refuses to sleep in her cot during the day for naps as well. She usually has 15 to 20 min cat naps in my arms throughout the day at whatever time she wants, which again means I don’t get to sleep either :(
Thanks in advance xx