I have arthritis and can occasionally get spasms in the knees and ankles, while sleeping. If I ice those joints, before sleeping, I usually have no problems. Now, after 2 weeks on Amoxicillin, I find it increasingly difficult to sleep more than hour at a time, because of spasms that affect joints as well as run along the long muscles of leg (such as a spasm at knee includes twitching/painful spasm 12 inch above and below knee.) This happens, even though I have been icing my knees and ankles before bed, as it has worked as a preventive in the past. I've read the typical side effects and realize it does not include the above situaition. But, I am suspecting that my use of Amoxicillin therapy may be cause of problem as my normal daily routine/activities have not changed since beginning use of the antibiotic and that the present level of discomfort radically affects ability to sleep!