Pregnancy can lower your immune system. Cold and flu like symptoms are very common. Tylenol, Ricola drops, tea and rest are the best remedies.
On my safe list: sudafed, benadryl, Robitussin-DM, Claritin, Tylenol.
It's quite possible that you are not, sick at all. Pregnancy increases all of your body fluids, so extra mucous/phlegm can be a product of that. Just relax and take it easy, I've had a stuffed nose for about 10 weeks now. It's frustrating, but there isn't much I can do about it.
You should ask ur doctor. I know that any pill can harm the baby.... Don't take if the doctor does not give permission!