New job stat?

Ok, I've worked at a local jail for about a year now. It is very fast-paced and hectic and very rare that there is any downtime, usually only on weekends or holidays. Anyway, it was overwhelming at first, then I kind of got into the groove at about 4 months or so and kind of like the way the time flys. But lately it has gotten very stressful again. I have gotten written up a couple times for mistakes recently. I'll admit one was somewhat serious, but nobody got hurt, but the other ones are kind of nit-picky if you ask me and would'nt be that big of deal in say a nursing home or hospital. I hear today that some of the other nurses and security don't have any patience for me anymore and one nurse said I should start looking for another job as a heads-up. I know I'm a little slower than some of the other nurses and don't usually make decisions as quickly, but I have improved this year. I guess they think I should have improved quicker as another nurse that started when I did. I think some of them are mad because I rarely help them out because I can't get my work done on time. I don't know some days go smooth, but when things get hectic, I feel overwhelmed and not sure what to do first. Yesterday was awfull. I really felt like walking out, but I need the job. Its not quite FT, but almost and I have another PT job ever other weeked and just lost my other PT job due to the economy. I'm not sure what to do now. It feels like some people are out to get me fired there. I know its not good on your record to get fired. I don't really want to work in a nursing home (like my PT job), but it isn't as stressful. What do you guys think? Think I should quit before I get fired or talk to the DON or something to tell them whats going on?