That's normal called sleep regression

It is very normal because your baby is entering into sleep regression milestone phase.

If your 4-month-old is having trouble sleeping, it’s common, as sleep patterns are still developing. Here are some possible reasons and solutions: Possible Reasons: Growth spurts or developmental milestones: Around 4 months, babies go through big changes (often called the "4-month sleep regression"), which can disrupt sleep. Hunger: Babies may wake more if they need feeding. Discomfort: Teething, gas, or a wet diaper might be causing discomfort. Overtiredness: Babies who are overtired may actually sleep worse. Day-night confusion: Some babies mix up day and night patterns. Tips to Improve Sleep: Consistent bedtime routine: Gentle, calming activities like a bath, soft music, and dim lights. Daytime naps: Make sure your baby gets naps during the day, so they don’t get overtired. Feed before bed: Ensure your baby is well-fed, but avoid letting them fall asleep while feeding. Create a sleep-friendly environment: Dark, quiet room with a white noise machine if needed. Watch for sleepy cues: Yawning, rubbing eyes, fussiness—put your baby down when they’re drowsy but awake. Avoid overstimulation: Especially close to bedtime. When to Seek Help: If your baby isn’t gaining weight properly. If there’s excessive crying or discomfort.