Did his temperature drop at all with the lukewarm bath and Motrin?
What other symptoms does he show (e.g., vomiting/diarrhea, runny nose, cough, grabbing at ear, rash)?
When did the fever start?
Is he still drinking liquids and making at least one wet diaper every 8 hours?
Strep throat below the age of 2 years is unusual.
Was he exposed to it somehow?
Did the doctor confirm this infection with a rapid strep test?
What antibiotic is he on?
OK, unusual diagnosis, but confirmed...and on amoxicillin, a good treatment choice.
It usually takes about 2-3 days of antibiotics for one to see clinical improvement, especially with the fever. You may think of the fever as a protective mechanism by which the body makes itself unsuitable for the infection. As long as he is taking in enough liquids to urinate at least once every 8 hours, then he is probably not dehydrated, even in the presence of a fever. The Motrin may be contined three times a day if there is fever or discomfort. Even if symptoms improve quickly, be sure to take the entire antibiotic course, otherwise you risk the serious complication of rheumatic fever due to incompletely-treated strep infection. If his fever rises to 105 degrees Fahrenheit or higher despite the Motrin and 10-minute lukewarm baths, then he should be evaluated by a physician (this is not a dangerous temperature, but it merits a recheck in the face of antibiotic therapy). Avoid alcohol baths or anything that may cause a chill since such may cause a higher fever spike.
Another option to manage fever involves alternating back and forth every 4 hours between Tylenol and Motrin (e.g., Tylenol at 12 midnight, Motrin at 4AM, Tylenol at 8AM, Motrin at 12 noon, Tylenol at 4PM, Motrin at 8PM, and repeat the cycle). The two medications are safe to take together and both work against fever/discomfort. Again, focus on hydration, and contact the doctor if the fever does not improve after 2-3 days of amoxicillin. Be especially good with your own handwashing, otherwise you risk catching strep yourself!