New mum seeking advice from experienced mums. Baby is 12 weeks and has just started behaving 'cranky' when she wakes up in the mornings. Up until last week she was at her very best in the morning - rested and smiley just after first wake up and loved playing and cuddling before morning nap. Last few days she has woken up cranky. This is in spite of sleeping very well and starting to sleep longer without waking for feeds. It's similar behaviour to crankiness in the evenings before bed - she's not hungry, not wet but nothing pleases her and I can't work out what she needs. She doesn't want a feed when she wakes and doesn't seem hungry (up until last few days she would always want a feed first thing). She's not bawling her eyes out or anything, just grizzling with the occasional cry. Once I put her down for her morning nap she naps ok.
Is this just another stage of unexplained baby behaviour or is there anything I can do differently?