If you are depressed, then please go to see a doctor. She/he will either diagnose you her/himself, or refer you to a psychiatrist or a psychologist.
Both a G.P. and a psychiatrist have the authority to prescribe you sick-leave. A psychologist does not.
Depending on the kind of medical insurance you have taken out, you may have to go through a G.P., or you may be allowed to go to see a psychiatrist directly. If you are uncertain about this, you can phone the helpline of your medical insurance (phone number usually on your card) and ask.
Whether or not you are obliged (by your medical insurance) to go to a G.P. first, it can sometimes be quicker, as there may be a waiting period of a few weeks, to see a psychiatrist, especially if you do not speak the language.
Here's a site to find a psychiatrist, if you don't get a recommendation from a G.P.
https://www.psychiatrie.ch/sgpp/pati...che/solothurn/. You can select by language.