For the last few days, I have 2 out of 3 pain at right side of head / headache. It feels like throbbing pain as per intervals. What could that be?

There are several. types of headaches, sinus headaches being one of them, muscular tension, and vascular are others. You won't know what you have going on until you see your doc. He/she can rule things out and identify what is happening and treat if needed. Consider biofeedback or clinical hypnosis ( if they continue. Peace and good health.