Seek help. There are many things that you can do to help yourself sleep before using medication. They are called "sleep hygiene techniques" and include things like avoiding stimulant like chocolate, tea, and soda late in the day and regulating your light exposure. Consulting your doctor would be a good idea to learn more.
See a Doctor. Not sure what alganax is. You need a thorough evaluation asap. Meanwhile, melatonin may help a bit but don't do this instead of being seen.
Sleep hygene. We r creature of habit , sleep hygiene is very useful tool to help u sleep , sleep medication can be used for a short period if time on as needed.
Check with your PCP. It is important to check with your primary care physician first - to assess your general health. If nothing is wrong and you are still depressed, he may try anti-depressants, like ssris, or if your depression is severe enough, refer you to a psychiatrist.