Venting ... and help is needed

This is probably going to end up long, so I apologize now. I don't know exactly how to proceed with what is going on at my job. I work in a company that is very small. There are 17 of us total working here (including our CEO & VP). We have 3 managers under them and then the rest of us. I work at a collection agency, but I am not a regular collector on the phone. I have been working as a legal secretary handling paperwork that is sent to our attorneys, keeping the attorney's calendar, filing paperwork, and going to court if needed for help. I worked at the courthouse before this job, but was let go because of budget cuts and I had been the last one hired. I got this job because a lady who works here as another legal secretary (my manager now) saw my work at the courthouse and recommended me. I was told when I started here I would be working what we call the "out of county route" and handling all the legal stuff for this. My manager handles the county we work in, because it is larger than my counties combined. When I started it was in shambles, and it took a couple months to get everything organized and running smoothly back here. About that time, things started going down on the in county paperwork, and it never got better. After they realized how hard I was working, they decided to put another job on me, without asking my input or anything. Then, in December, they decided to make me run my out of county route, the job they gave to me a few months ago, and help with the in county route and get it cleaned up, because my manager couldn't do it. I basically started getting all of the work no one wanted to mess with and when I tried to express my overwhelmed feelings, they wouldn't address it. My manager is very passive and I don't think she takes my input into the meetings with her to our CEO and VP.

I have recently gotten used to the fact that I am obviously going to be the one they throw everything on and have tried to remain positive that I at least have a job. Well, the CEO left for vacation last week, and it was implemented that I now must take phone calls (like a collector) as well. I kept telling my manager I was not just venting to her and that this was a problem, but nothing has changed. I am tired of doing all of these different jobs without anyone asking my input beforehand. I did not take this job to be a collector, and I did not take it to be a customer service person (which is what the job I took over should be in). Our CEO does NOT like to handle confrontation, so I know I can't just go in and talk to this person when they get back from vaca, so I am contemplating a letter. Is this the right thing to do? I am going to look for another job, but I want my input to be heard at least, so maybe, just maybe, it will get a little better until I find something new. Should I do this? I plan on sending it to the VP and the CEO and also to my manager so she knows exactly what is going on, too. I don't plan on telling them about my job search. I just feel as though I am not valued here, and I am just being taken advantage of because I am eager and willing to help. But this is just too much.

Can you help? I'd greatly appreciate it!