Constantly thinking about only one thing

Hello dear, The symptoms mentioned by you here of depressed/low mood, reduced sleep, negative fixed ideation, crying episodes, unchangeable mood, and not being interested by previously pleasurable events are all suggestive of an ongoing depressive episode. However a comprehensive assessment is definitely required to confidently comment about your condition. Assessment is also required to understand the biological, psychological, and socioenviornmental correlates of your condition. Medical factors like thyroid, anemia, vitamin deficiencies, etc will need to be assessed along with a detailed psychological understanding. Howsoever please be assured that your condition can be helped with proper mental health management. Depression is a reasonably common and treatable condition, so please do not lose hope... A combination of medication and psychological intervention is likely to be well suited to your condition.. Hope this helps you. Best wishes for your health and future...