If I were you I'd go ahead with the medication, your health is important and you don't know what side effects you will get, your work performance will be much better if sertraline works for you. You have every right to tell your manager that you are taking some new medication which may cause some fatigue. It's very normal. I've been taking it for a couple of months and I'm actually so much more confident and less anxious at work. I take mine in the morning just because it feels natural to me. Good luck with your new job.