Ugh. How annoying!
Have you tried flushing out your sinuses with salt water (using a neti pot, or saline drops, or DIY methods, such as a bulb syringe or small cup)? I find that to be SO helpful when I have congestion... and also, those nasal strips they sell that keep your nose open are a G-dsend! I've been wearing those lately, and I'm not even that congested, just a little...
I hope you feel better soon!
(BTW, I do know someone who had the flu when she gave birth -- she had a homebirth in the late 70s. It was her second homebirth, so she knew what to expect, pain-wise, but she got the flu and she said it was one of the worst experiences ever -- not the giving birth part, but the having the flu part. I guess she nearly passed out a couple of times for lack of oxygen. I hope hope hope this never happens to anyone else! Most of the other very pregnant women I've known have gotten over their cold or flu before going into labor...)