"Because I went to bed past midnight, and then I couldn't sleep.
Explanation:
This conveys a clear message that he/she is tired because he/she could not sleep past midnight; therefore, they were awake from 12:00 P.M onward and that is the reason that they're sleepy.
so can make the sentence into a compound. and too but it isn't worded or punctuated correctly. Because would make the sentence more complex. So is the proper way to word the sentence.
