What Causes Severe Irritation And Depression In A Person?

I had a good childhood but im lavking of self esteem most of the time unyil now. I easily get irritated and most of yhe people call me pessimistbut I always tell them that I m just being realistic. I laugh with friends but there are times that I m just quiet even if im with them or at work and thinkingvof things that makes me more sad. I am often sad specially when my grwndmother died three years ago and until now I still cry in my room and can t accept the fact that she s gone. My situation got worst when I got fired from my job last december where I worked for more than two years and it really made me feel small, I was fired because I have been accused on a thing that I didn t do and it is the first time I got fired. Now I m far from my friends and lost some as well because of the sadness I m feeling I think that its much better not getting intouch with them since I m just a burden for them (that s how theyvmade me feel sometimes) and I got a new job but I m not happy but keep on trying to like it just to earn. These past few days I m thinking of having a suicide since it is the best solution for everything. I already told my aunts about it but they don t take it seriously but now the desire I have to kill myslwf is gwtting atronger and stronger and it also scares me but I cannot control it. Its the best solution for everything and I don t have any purpose anyways. I think I have a depression. I wanna seek a professional advice but I can t afford one infact I got lots of debts and it is one of yhe reason why I wanna die. I really hope yo get a response soonest