waking up in the middle of the night

My baby have been waking up in the middle of the night crying. At first i thought she's hungry cos she cries really hard but after doing her milk she just rejects it. It happens at like 4plus every night these few days. I gave her gripe water and massage her every night before she goes to bed so i rule out colic. She will be 5 months nxt week. What could be the reason?