A fever is not necessarily a bad thing - it's the sign that the body is fighting something off. Regardless of whether the temp is 100.5 or 102.5, the same mechanism is at work - whether it's a virus or a bacterial infection (with the obvious exception of someone being so overdressed that their body temp is raised without an illness present). So having the immune system react is a good thing. That's why most doctors don't want you to give anything to reduce the fever at 99 or 100, even up to 101, unless there is a compelling reason to do so.
Reducing a fever with any medication is only beneficial if the person has symptoms that are uncomfortable - aches, significant sweating, headache, sore throat, etc. - or a very high fever. I'd have given meds at 102.5 like you did because he was uncomfortable, but I don't think the goal is to get the temp back to 98.6 - that doesn't mean the person is well, it just means the meds have reduced the fever.
I think you have to go by your child's symptoms as well as by the rules of the preschool or day care. It's just so hard to know if the child will bounce back in a few hours and be fine (with or without meds) or if there's something else afoot. When I was teaching, we had tons of kids arrive with low grade fevers or mild belly aches who were in a full-fledged meltdown by 9 AM, complete with high fevers and vomiting. It was so frustrating to have a sad/sick child waiting for Mom to come collect him, while the custodian was cleaning up the floor from the throwing up! But it's also frustrating for the parent who took the day off work only to have a healthy child running around the house before lunch.
If he wakes up shivering, it could be that he has been sweating during the night - the body releases sweat to cool things down, but then the wet child gets cold. But since needed to sleep and it took you a few hours to get the fever down, he probably was fighting something off. You can increase his fluids, but there's not much else to do in the moment. I think you can reduce the fever to the point that he is comfortable, but it's possible you could have accomplished that by stripping off a layer of clothes (especially if wet), giving him water, and letting him sleep. Don't keep using up the meds to get it down to 98.6. If it goes back up again, you just reduced the fever artificially without actually doing him any good.
There is plenty of research on immune system boosting that helps a lot of parents. There's a lot of expensive junk out there that has no proven benefits, so don't waste your money on stuff you see commercials for (vitamin C, this berry or that fruit, some children's vitamin chewable, etc.). There is solid research on a natural peptide given in a balanced supplement, but that strengthens the immune system over time. You can't give it the day of and expect results. The trick is prevention. In my work I've seen tremendous improvement in overall health, and my own family hasn't had a sniffle in over 5 years. But it's a sustained effort.
The only other thing you can do is to look into some programs where single parents can park "slightly sick" kids for the day, where everyone has something going on and there are health workers/nurses on staff. These are usually very expensive though. Alternatively, if someone you know wants to do "occasional" day care and sit with a slightly feverish child but not be booked every single day, you might get lucky with that.
So sorry - I know it's so frustrating.
