pregnancy or the flu?

I finally got over my first trimester symptoms (fatigue, morning sickness) around 17 weeks, but I feel like they've returned. I'm 21w5d and have been feeling exhausted over the last few days! I also have nausea that comes and goes, although not as bad as the morning sickness was at the beginning of my pregnancy.

Is it possible to have these symptoms again this far into my pregnancy? Or could I be coming down with something like the flu?

I see my Dr. on Thursday, so of course I'll ask him, but just curious if any one else has experienced this? Thanks!