It sounds like you may be experiencing a migraine. Since you have already taken ondansetron to control the vomiting, you can safely take paracetamol (500 mg to 1000 mg) for pain relief, as it is gentler on the stomach than other pain relievers. Rest in a dark, quiet room and sip water or an electrolyte solution slowly to stay hydrated. Avoid heavy meals for now. If your headache worsens, does not respond to paracetamol, or is accompanied by neck stiffness, vision changes, or high fever, please seek immediate medical evaluation.