Running a round can make anyones temp rise. I would take it at times when he is not as active to see if it is consistant. A fever is also a good thing because it means the body is doing its job to get rid of any toxins or virus that may be in his system. Keep track of any additional symptoms and keep a diary for your reference.
Be aware and prepare:
I also recommend doing some additional homework on vaccinations. This is the age that some children have severe reactions to vaccines. I do not want to scare you or anyone else. I just think it is so important to be informed and not just take some ones word on something even if it is your doctor.
It use to be 1 in 100,000 children had autism and now its 1 in 150 and may showed signs after their 18 mo well baby visit. Is it more that a coincidence that the vaccines recommended increased over 300%? That is what got me to dig.
I just want parents to be informed and know that they have a choice. You can postpone any vaccines until you have more information. It is not a law to vaccinate, it is a requirement for school and some day cares.
HTH