Need some encouragement

I have been a nurse in a LTC/Skilled nursing home for 2 years. (I graduated nursing school in 2007 at the age of 49) I am the oldest nurse on the unit. I also have ADHD, (which is controlled by meds), I have IDDM, and also a heart attack survivor with an ICD. I received a call from my unit manager that one of my patient's INR is low, and she inferred that I was not giving the coumadin. I give all of my meds all of the time. She said that she may start counting the comadin. She also said that if she had to count and find out that I was not giving it, I would lose my job. So- I saved her the trouble, counted the coumadin for my patients, had the RN supervisor verify the count, another nurse verify that I had the dosage needed, and that I had administered it. My appraisal stated I was not good at time management, (I was labeled because of my adhd) because sometimes it takes longer than the 8 hours to get everything done, if extra things come up which need attention. Nothing is said to the others that work overtime. I was told that someone watched me do something and said that it took me 1/2 hour (which I guess was unacceptable), but that time the person spent watching me took 1/2 hr of their time where they could have been doing something else. I am the nurse that has been singled out to write up for petty things. It is hard for me to find work elsewhere because of where I live, and I do not want a long commute, and there is no facility that can match what I make. I get assigned the straight caths, stool samples, hemoccults, from the other shifts, because they decided that they did not want to do them. I am a good nurse, I can assess my patients, but I am treated as though I am not smart enough to do things such as admissions, mars and tars (I have to go and clean up the mars and tars on the 1st because of all the changes that were missed). I also found an antibiotic IV that was not given for 8 days,(fortunately it was not on my shift) because the admitting nurse wrote the generic nameon the MAR and pharmacy sent the brand name. I was the one who took the time to call pharmacy to find it out.
Our stat med box is supposed to be locked, every day I come in and it is unlocked. I lock it back up, told my boss it is unlocked every day. We had an inservice regarding this matter, with the threat of corrective action if it is found unlocked. My boss tells me, "that is why you are here, to lock it back up." I get no complaints from families or my patients.
My hall does not look like Christmas, with call bells blinking on and off . We keep the patients happy. I love what I do, I am just tired of being treated as though I am unable to handle my unit, and that I am dishonest, and that I am not smart enough to do things such as order labs, or do an admission. I am going to speak to my boss, let her know how I feel about her not being confident that I was giving meds. She will probably say, " looks like you got hemocult #1, the stool sample for C-Diff, and the caths for UA C& S, way to go." Any encouragement/advice would be helpful.