24 weeks.... All I can do is sleep.

Not in a good way. I'm exhausted. I am so exhausted and I haven't done anything. Today is so bad I just want to cry. I am a stay at home mom and I can't say a job has me tired. My son is 6 and he doesn't require much energy at all when it comes to taking care of him. I literally cannot seem to stay awake for long. If I do it's because I have resorted to drinking coffee.... And not just 200mg of caffeine... Lots more. That's the only way to stay awake and I obviously don't want to do that daily. Today I woke up at 12:30pm I managed to stay awake until 2pm and fell back asleep. I just woke back up and it's almost 6pm. I could go back to sleep right now if I wanted to. My dog actually woke me up. Why am I so tired? No idea because yesterday I slept all day. There are no words to describe how bad I want all this fatigue to be medically related. I go back to the doctor on the 25th and will demand some blood tests. I take my prenatal vitamins daily and never forget to take them anymore as I have a weird phobia of thinking im causing this fatigue and I want to be completely sure it's not my fault. Which lord knows it can't be. Anyone had any similar situations and was there a reason behind it. Medically or life style reasoning behind it? Please share.