Lowering my dosage

I have been told by my doctor to lower my sertraline dosage from 150mg to 100mg. i don’t know if I’m just not feeling well or these are side affects but I’ve a horrible migraine for days , really bad nausea, sleeping all the time. no painkillers or amount if water i drink is helping . is this the side affects to lowering my dosage ? or am i just unwell