You seem to be exhibiting the signs of depression including: difficulty concentrating, inability to focus, memory problems, irritability, emotional dysregulation, and lethargy. Depression makes sense in the context of losing both your best friend and fiancé. You have endured two major life losses. Your reaction is understandable.
You have asked two questions, one of which is “are you being lazy and simply not wanting to work?” In light of your recent losses I highly doubt these explanations would be accurate. Depression seems like the more logical explanation.
Your second question is related to whether you should visit a psychiatrist. Yes, you should see a psychiatrist and a therapist. A psychiatrist can evaluate your mental health condition and determine whether psychiatric medication would be an appropriate form of treatment. A therapist could help by engaging you in talk therapy. Both could benefit you greatly.
You also mentioned that you have several ongoing medical problems. These should be evaluated by a medical doctor. Don’t neglect these problems. They may be contributing to your recent difficulties.
Receiving professional mental health treatment would be the most efficient way to deal with these issues. I’m sorry but I am not familiar with the mental health resources in your country. Hopefully there is an easy way to access these services. Please take care.