A.,
so much info to give but unsure where to start. So here goes.
Your son should be in a REAR facing seat not only to the weight limit but more importantly until he turns ONE YEAR OLD. The age limit is for bone development and if he were involved in an accident in a forward facing seat, severe and life threating injuries would occur ...
"Infants don't have many body parts that are strong enough to withstand crash forces, so the rear-facing car seat distributes the crash force along the entire back, neck and head, putting less stress on any one part of the body. The infant's head, which is large and heavy for a still delicate neck to support, is also better supported with a rear-facing car seat. The incidence of severe head and neck injuries for babies is greatly reduced in rear-facing car seats. The baby's "ride-down time," or the time it takes to come to a complete stop, is also lengthened, which reduces injuries by reducing the body trauma from a sudden stop.
The additional support plus the manner in which a rear-facing car seat "rides down" in a crash gives your baby the best chance for survival and less chance of injury in a crash. The simple way to estimate crash force is weight times speed. So a 10-pound baby in a 30 mph crash would experience 300 pounds of force. A rear-facing car seat spreads that 300 pounds of force over a greater body area, causing less injury to the baby."
If he is in the proper facing seat and if not ... seek the nearest safety council as they will assist you for free, in safe ways to transport your child. Most people (70%) fail to install and use care seats appropriately and well that makes it as bad as not having one at all.
The site to find your local center is http://www.seatcheck.org/
And the rest of the help is that you probably do need a new car seat and the money is well spent since it is the safest thing you can ever do for your little one when you realize how much time you travel and the number of accidents and fatalities from motor vehicles.
I personally prefer Graco and found there safety studies great so I chose the Graco SAFESEAT (step one, rearfacing for infants) not the snugride as the safeseat went to 30lbs and the snugride to 22lbs. And well my princess was a porker and we needed that extra as most people do. And I did not get the convertible seat just because I plan to have more kids so they will all get plenty of use and mostly because I did not find the safety ratings as high for my most precious cargo.
Now that we are past one year we have moved up to the Graco SAFESEAT STEP 2... it's forward facing and has the ability to recline back in 2 additional positions. And it was only $129.00 at http://www.toysrus.com/product/index.jsp?productId=2507896. And again...money well spent.
If you are on a fixed income and can not afford the necessary seat.. ask the safety center near you about income based help to get a seat. they sometimes can get you a discount or a voucher.
Hope this helps to keep your baby and others safe. -mb