Where am I going

I don't know what to do with myself, and what to do with my professional career. I am in a position at the moment, where I work for a very good company, that looks after its staff members. I sell a really good product, that almost sells itself. The problem is I am not enjoying my job. The basic day to day function of my job is so frustration, that I find myself on Monday mornings wanting to cry when I have to go to work.

I cant help but think, every day, that I do not want to be in this same position when I am 35 or 36. I do not want to be a 35 year old sales rep who is still trying to get 20 sales calls a week of new business. Where am I going to find the new business in 2 or 3 years time. I am feeling so frustrated and upset, because I really don't know what to do. I am not a corporate new business executive. I am a Key Account Manager. I like looking after accounts and making sure the relationships are strong and keeping business.

So my issue at the moment is, do I go for another job, again, where I have the job description that I enjoy and I love my job, but I might not have the great treatment or great company I work for now. Or do I stay at the great company that really looks after me, with a fantastic product, but I hate my job everyday....