Buy some melatonin at costco/price club and take it at night for sleeping. If it works, it will give you a good idea if you are lacking melatonin.
Quote from Melatonin Miracle.
" An excess of serotonin and shortage of melatonin has been linked to some forms of depression and mood disorders, In fact, a number of psychiatric drugs , including Prozac, are called serotonin uptake inhibitors beacause they maintain normal
serotonin levels and stimulate the production of melatonin".
My hubsand takes melatonin and it works great for sleeping.
An excellent doctor can diagnose if you have any depression.
Also, I have found out from personal experience that severe allergies and asmtha can mimick depression.
Glad to see you are posting about this and getting nice responses..