Why did Moshe address Hashem with the Name of Adnus, and not with the Name of Havayah?
Ramban: Because he understood that Hashem would not do bad to Yisrael with the Name that denotes Rachamim, only with that which denotes Din. 1
He did the same thing earlier, twice (in Pasuk 10 and in Pasuk 13, either in order to stave off the Midas ha'Din, or because he was afraid to use the great Name of Hashem that had only just been revealed to him (Ramban).
Seeing as Moshe was not currently Davening to Hashem, what business was it of his how Hashem treated Yisrael?
Rashi and Seforno: He was complaining that Hashem had appointed him to communicate with Pharaoh, and that he was the Shali'ach through whom Yisrael was suffering. 1
Rashbam: He wanted to know that if Yisrael were not worthy to be redeemed, then why did Hashem send him in the first place.
Bearing in mind that Hashem had already informed him that Pharaoh would not allow Yisrael to leave, what was the basis of his complaint?
Ramban (citing the Ibn Ezra), Riva: He thought that once he approaches Pharaoh, things would begin to get better - not worse.
Ramban #1: He understood that when Pharaoh refused his initial request, Hashem would start punishing him, one stroke after the other, until he relented, but not that the Shibud would get worse. Consequently, when three days 1 passed and Hashem did nothing to stop Pharaoh's new decree from taking effect, he thought that this was a long time, and voiced his complaint.
Ramban #2 (citing Midrash): When Pharaoh issued his latest decree, Moshe returned to Midyan, where he spent six months, 2 whilst Aharon remained in Egypt. That is when he returned his wife and sons to Midyan. After six months, Hakadosh-Baruch-Hu appeared to Moshe and instructed him to return to Egypt. He then left Midyan and Aharon left Egypt, and they met outside Pharaoh's palace just as the Jewish officers were leaving. 3 The gist of Moshe's complaint therefore was why Hashem sent initially him on a fruitless mission, seeing as He intended to redeem Yisrael half a year later. Because if the trend continued, Yisrael would be totally destroyed.
Alternatively, a long time elapsed from the time that the Jewish officers were smitten until they gained an audience with Pharaoh and from the time that they gained audience until Moshe complained to Hashem (See Ramban). Also refer to5:22:3:3.
Others say, three (Ramban).
The Midrash compares to a deer, which one moment it is seen, and then it disappears, to reappear again later (See Ramban).