Why does it say "b'Derech Mitzrayim"?
Rashi: It is like I sent against you in the Midbar, when you left Egypt.
Radak: They went to Egypt to bring grain, due to the hunger. You did not think that I bring the hunger against you, and you did not repent to Me!
Malbim: It is explained in Hoshe'a that many of the 10 tribes went to Egypt at the time due to the afflicter's anger. Hashem sent a plague among them ? "Mitzrayim Tekabetzem Mof Tekaberem" (Hoshe'a 9:6). This was the fourth time that He sounded the Shofar. Melech Ashur came against them on the road and killed them with the sword - Efros Aleihem Rishti?; Yipelu va'Cherev Sareihem" (7:12, 16).
Why does it specify "Bachureichem"?
Radak: They sent bachelors to bring grain.
Why does it mention "Im Shvi Suseichem"?
Rashi: They will kill also the horses.
Radak: The enemies on the road killed Bachureichem who were riding on horses going to Egypt or returning from there; they plundered the horses.
Malbim: The horses will be killed with them; part of the stench is due to them.
What is the meaning of "va'A'aleh b'Osh Machaneichem uv'Apechem"?
Rashi: The stench of your dead bodies stinks in your noses ? I raised it.
Radak: Your camp that went to Egypt, they were killed on the road. Your bodies decayed and were a stench to passersby. The stench was also in your noses, for camp after camp went to Egypt, and the later camps found the earlier ones killed - even so, "v'Lo Shavtem Adai"!
Malbim: Since the stench ascended also in your noses, there was a plague that spread also to Eretz Yisrael. With all this, "v'Lo Shavtem Adai"!