Since I was a teenager (a very long time ago) I suffered from allergies to grass, trees, dust, pets and more. To help with this, I took a Loratadine tablet every day. Lats week I wondered if the alternative (Cetirizine) that is easily available might be more effective. It was more effective, or seemed to be, but after about two weeks on these, I seemed to be becoming depressed so I did some research. And yes, antihistamines are associated with depression.
I have now chosen to stop all antihistamines and within a few days the depression lifted and I feel completely different. So, if you are taking antihistamines and also feel extra tired or depressed, try coming off them for a while and see what happens. The worse you might get is a lot of sneezing, the best is a new life.