Here we go again

School started about 2 weeks ago and I already feel overwhelmed. I'm only taking 12 credits but it's enough to keep me very busy. I'm taking Organic Chemistry I, Genetics, and Physical Anthropology. The classes are great and I enjoy reading the material, but holy hannah... there's a lot to learn, and not enough time to do it.
My work schedule also changed, so now I work friday and saturday night, off sunday, then again monday and tuesday night. Sure, I only work part time and I have 9 days off bi-weekly, but it kills to work that many in a row. I did it to myself, hoping that I would be able to spend the weekends with my family, but I still spent the whole day two saturdays ago at the county library doing homework... and I still didn't get it all done. I get more accomplished while I'm at work- good thing I'm expedient with my work load, but I'm very tired, especially on the tuesdays that I work. Working all night, then sleeping for just a few hours, then going to class, then going back to work for another 12 hr shift is draining. But what do you do, right?
Being pregnant and taking care of a toddler and going to school full-time, as well as working and doing volunteer work has been... well, tough. I thought I'd be able to handle it like I used to, but man, does pregnancy just drain every ounce of energy out of me! I was on Metoprolol for my heart condition that I get with pregnancy, but it made me so sleepy I couldn't even function. I had four meltdowns in less than one week because I couldn't keep my eyes open and still had to study and do everything. It was awful. Now I'm on Digoxin and it's been great, but still I suffer from fatigue from the pregnancy itself, and it's hard. It's not that I don't wish I wasn't pregnant, because in reality, if I were to have a second child any time in my life, it would have to be now anyway, it's just that with everything, it makes it nearly impossible to get anything accomplished. I feel like everything is derailing out of control again- it's like trying to keep a mudslide from sliding further down a hill- and I'm not sure how to get everything under control. Maybe I am doing too much, maybe not. Maybe I need more energy to keep going during the day... or maybe I just need to stop everything and just work... go to school when the kids are older... *sigh* I guess I get discouraged because I'm not a straight A student like I wish I was. My GPA is not that great- still okay, but not above national average for medical school applicants- and that bothers me. I don't know if the medical school committees will look at my application and say, "Her grades aren't the best, so we'll skip her for now" or "Wow, look at what all she's done, and even though her grades aren't the best, she still managed to keep doing everything else through her personal responsibilities." I hate these moments. I wish I could look into the future and figure out where I'm lacking so I can do better. I want to be a great mom, a great student, a great wife, and a great worker, but apparently I'm not super woman, and can't be great at everything. That's depressing.
Aside from school stuff, life at home is okay. We moved this last summer into a house with central air. Can I just say how much of a blessing that is? I love central air. It's like... I can live in Alaska-like conditions if I want haha My son is in daycare for 20 hrs/week, while I'm in school - that's really roughly how many hours I spend just going to school and sitting in class, totally absurd... He really enjoys it and looks forward to going and always says how much fun he had with "Missa" (Melissa, his teacher). I'm glad he can get away and socialize with other kids and not be home all the time. It's affordable as well, which is a nice plus.
Anyway. I think I'll stop for now. I just had to get on here and write something just so I can get everything off my chest. I'll write again another time.