My 8 Month Old Is Whimpering All the Time!

Some teeth especially the canines (or eyeteeth) cause more problems then the others. Both my boys had diareah and ran a slight fever when they can in. But if nothing has changed in his diet and he is pooping regularly and has been like this for more than a few days, I would trust your insticts. Get the baby, get in the car now and go to the nearest children's hospital er. If he is normally active and now sleeps something is not right. Act Now. Good Luck and let us know how things turn out.

I would have thought constipated, but if he got the okay from the doctor that's probably not it. He might just go through a different stage. Does he act like he is in pain when he whimpers? If not, he might just have discovered a new noise and really likes it. Whimpering to him probably doesn't mean the same as to an adult.
Hang in there, it will pass.

I would say your baby is uncomfortable in som way that your Dr. can't see. And I would take him to a chiropractor and have him adjusted it may just help.

Is he having his regular amounts of pee and poop diapers every day?

I too suggest a chiropractor. A good one will be able to adjust an infant with no issue. My daughter has seen a chiropractor since she was 4 days old. :-)

You may also look into a Homeopathic doctor or a Naturopath. Often times they will look into things a traditional doctor won't and will give you ideas of things to look for.

Keep in mind you have mothers instinct for a reason. I have read and heard story after story of mothers who KNEW there was something not right (big or little) with their little ones even though the doctor kept saying no, everything was fine. The mothers were persistent and finally the problem was identified. If you believe in your gut something is wrong, keep looking for someone to help you until you get answers. It bothers me that you say he isn't eating like he normally does. Most infants do not have a slow down until after their 1st birthday. Most often it is increased eating patterns due to growth spurts and such. The sleeping could be related to a growth spurt, but keep an eye on it.