3 medication errors in 7 months!

I know, I know...most of you must be looking at this and thinking I'm living it and I feel the same way. I'm posting this because I really need some advice; I'm depressed, confused, feeling incredibly stupid and very guilty. Let me give you the scenarios and you can tell me what you all think. By the way, in case you can't tell...I'm a new grad, June 2005:

1) First medication error occured when I gave the wrong patient the wrong medication (I did a stupid thing by carrying two patients meds at the same time). This patient happened to be a chronic pain patient, knew the medication wasn't for him but accepted the medication anyway. The medication was Percocet 5/325. I alerted my charge nurse right away, told the doctor (who started laughing and told me not to worry about it because this patient was on so many meds the percocet wouldn't do anything to him.), and wrote out the incident report. Went home that day feeling terrible and wondering if I'm really going to be good at this.

2) Second error: received report from Step-down unit, was told this patient had not received his evening dose of Coumadin. When this patient came up to the floor I looked in his file to see if the Coumadin had been given, couldn't find the documentation in the usual place, called the nurse back in an attempt to find out whether it had been given or not, later found out I was connected to another nurse who had also given me report that same night and who told me she had not given the Coumadin. Gave the patient 5mg Coumadin and then found out the original nurse had already given the 5mg!!! Once again filled the incident report and once again went home feeling terrible and wondering if I made the right decision to be a nurse.

3) Latest one: Received report from one of the nurse on my floor that the patients Unasym had been discontinued and the patient now had an order for Penicillin Q24hr, when I looked in the MAR I saw the registrar had picked up the order as Q24hr also, I signed off in the patients chart right under the registrars signature. To make a long story short, next day received a call from the charge nurse on days alerting me to the fact that the patient had missed 3 doses of her penicillin because it was ordered for Q4h!! Filled out another incident report, was written up for this latest occurence, went home and cried myself to sleep and have been feeling horrible ever since.

For the past 20 years all I've wanted and dreamed about was becoming a registered nurse, I graduated at the very top of my class, received the Gold medal at graduation, and am was hired at one of the top orthopedic facilities (which has Magnet status) in the nation right out of school. I can't help but wonder...what has gone wrong? I can honestly say, I've learned from each and every incident, but I'm beginning to wonder if I should quit before I'm fired.

Any and all advice will be very much appreciated. Thanks.