I was VERY overwhelmed second year. I struggled to get thru the material, I was stressed out to no end, and I always felt like I couldn't manage to get thru. But I did. Sometimes I didn't get the grade I wanted, and sometimes I got so overwhelmed I was unhealthy physically and mentally.
Remember that even though it may seem like you are the only one, some of your classmates feel exactly the same way as you do, you probably just don't know it. Some are probably in worse shape then you. It sounds like you had a bad day on top of hitting a bit of a rough patch.
You WILL get through it. It may not seem like it now, but you will. The sheer exhaustion is just catching up with you right now. Usually sleep and a night or two of (gasp!) vegetating in front of the boob-tube (post-exam) helped me to de-stress and gear up for what was next. Maybe skipping class to get more study or sleep time will help you? As others suggested, talking to someone in academic affairs or your dean of students may be helpful in giving you some peace of mind or getting you some help to enable you to get through. Maybe they can give you an exam delay to help you get back on your feet. Maybe you need a tutor or someone to help develop a workable study plan for you. Your school wants to keep you enrolled, and wants you to have good mental health---they will try to help you out, especially if explain you are at your wit's end.
Remember that things change third and fourth years. Yes, you still have to study and worry about things, but you only have one class at a time. You probably have longer intervals between exams. Every clerkship is different in terms of stress and work---there are some with long hours and some with relatively few hours and minimal studying requirements.
Take things one day at a time. Breathe. Take a jog if you like to exercise. Two years from now, I GUARANTEE no one else will care if you sucked it up on an OSCE during second year, although right now it may seem like it's one more thing to worry about.
good luck
