I nursed two babies within the last 2 years and have pretty bad allergies. You're in my area, so I can say the following!
My pedi told me that babies in this area CAN and DO have allergies. It is up north that young babies don't get allergies until older. He also said the fairer you are, the more likely you are to have allergies in the south as fair-skined people are genetically made up to live in northern climates-never heard that before but it makes sense to me!
That said, you CAN take Zyrtec (now over the counter) withOUT the decongestant (as this is bad for the baby and will dry your milk up) and it will be safe for the baby. It was approved by both my OB and my pedi while I was preg. and breastfeeding! There is even a generic for that now also!
Also, try baby vicks for your baby (the baby type is safer on sensitive skin-it says to wait until they are a bit older than your son to use, but it won't harm him my pedi said unless he shows a skin allergy to it and that can happen to anyone, baby or not, at any age! It is kind of tricky to find, so you may have to ask, but it is carried by Wal-Mart and I think CVS.
And there are the vicks and other brands of water-less vaporizers. And also, use the medicine trey on your vaporizer to put those methol vapors in the air to aid in his breahting.
If you can, put him in a bouncy in the bathroom with you, your family members or your hubby while you shower, or just simply run the shower on hot with the door closed and creat a type of steam room. Even if you or the others don't take hot showers, the moist air will/steam will help de-clog his sinuses.
And keep up on the saline spray!
If it gets really bad, ask your dr. They do have things they can give, but they just don't like to when they are this young. I think we got my son a perscription or were told to give him a certain amt of mucinex for decongestion at around the 8-12 week mark, so there is something they can do-they just like to exhaust all other natural methods before turning to meds at that age!
Best of luck!
T.