I’ve been taking sertraline for about 2 months. First month 25mg and then 50mg. Second month 75mg and 100mg.

I’ve felt really better this last month: less depressed, less anxious, more energy, I was really happy with these results.

But last two days have been hard, I feel tired and not well.
I know a drug can stop working after a long time but that’s only a month !

Should I worry??
Thanks for your help !