Thats silly that they are saying they can not get him in until friday the poor thing that sounds horrible. I would call again and say you need an emergency appointment.
Was the tick he found already imbedded? If it was, save it, too. It can be tested for various tick borne disease. If you didn't save it, then some antibiotics are in order right away. For kids, it should be amoxicillin for a month. If the doctor wants to "wait and see" or just give him a week or two, ask for the full month to make sure. Believe me, you do not want to risk him getting Lyme or other tick borne diseases. They are horrible! Not everybody gets a rash and sore knees, and if the early symptoms are missed, it will be much harder to cure later.
Definitely save the other things you found, too. It is possible they are engorged ticks. The nymphs can be quite small, and even when they swell up during a feeding, they don't always look like bugs.
Has your son been sleeping outside, its only after that anybody even your doctor, can come up with some kind of answer, sounds like a good puzzle for somebody to answer, then at the end of the day just were has he been putting his willy? a very good question, did he not fill anything bite him?
Good Luck, mysterious things do happen.