The only known side effects of amoxicillin (clavamox is a brand name of amoxicillin) are diarrhea and vomiting.
I would think that it could be caused by her having difficulty breathing due to the respiratory infection. Lying down can change the effect of any kind of breathing difficulty, often making it more difficult and labored.
If the tic keeps up, especially after her breathing is cleared up, then I would definitely take her to the vet and have him check her.
Meanwhile, while she is recovering, there is a great over the counter pediatric product that you can get to help ease her breathing so that she can relax. It is called Pedia-Sure Gentle Vapors. It consists of a small plug in device and rectangular card-like pads that fit into it. You plug it in and it emits a vapor of menthol, eucalyptus, camphor, lavender and chamomile.
I usually use it in the bathroom, as it is easier to feel the effects in a small room. Let kitty hang out on some towels or a pillow, plug it in and close the door (you might have to sit with her for a while if she doesn't like to be shut in alone!). It should make her feel better. You can also run a hot shower, the steam will also help ease her breathing.
It would be interesting to note whether or not the tic goes away while she is breathing the steam and/or vapor.
When penny took clavamox her side effects were drowsiness and uncontrolable bowel movements..