Hi J.! I know you are worried about your son. You have been given a lot of good advice below. I just want to share a few things to try to clarify some of what others have said. I am a 36 yr old SAHM with 3 kids (10, 7, &2) so I have a little experience with colds & cough. My middle one ended up at the doctor twice a week for her first year of life because she had every virus that came through her daycare and then chronic ear infections. We have dealt with fevers as high as 105 under 1 year old, vomiting, diarrhea, dehydration, tubes in the ears...you name it and I have probably dealt with it. But if you aren't sure about what you are getting here, please go to www.webmd.com. This is an excellent source of information on illnesses, injuries and medications.
Fever - Yes, alternate between motrin & Tylenol. Also, these are not made to eliminate a fever. If your son's immune system is fighting really hard, the fever may only go down a couple of degrees. This is ok. Pediatricians have differing views on how high a fever should be before you go to the ER. Some say 100, some say 105. Your son is over 1 so most at that age will say more than 100 for more than 2 days. But, they will also say that as long as your son isn't limp, lethargic, dehydrated and glassy eyed, he is probably ok up to 105 as long as there are no other symptoms of a bacterial infection. Most fevers are from a viral infection which no antibiotic will work on. All you can do is wait it out and make sure they are hydrated.
Hydration - This is ULTRA important! You can tell if your son is getting dehydrated by checking his diapers, checking his fontanel on the top of his head and looking at his eyes. His eyes and fontanel will appear "sunken" in his head if he is getting dehydrated. At this point, GO TO THE ER! Don't call the oncall doc...your kid needs an IV. But if his eyes and fontanel appear normal, and he is still having wet diapers, he is hydrated fine. To ensure that he stays hydrated, make sure he is drinking. Even if he doesn't want to. Someone mentioned getting the fluids in any way you can. Use an eyedropper if you have to. And whatever fluid he will drink other than milk. Milk is not good because it increases the mucous in his system (I think someone else mentioned this too). One time when my daughter had a really high fever (103 - 105), we were worried about it so we gave her 1 oz of Gatorade every hour. It was all she could handle (she was throwing up a lot). Her stomach wouldn't hold down any more than that. But it worked. As long as it is a liquid. Obviously some liquids are preferable to others but when you are worried about dehydration, get something in your child. If all he will drink is kool-aid, give it to him. It's better than nothing!
ER - I don't know what your insurance coverage is...but for some this can be a tough decision to make. If you are worried and would like to ease your mind, the best bet is the on-call doc with your peds office. Usually, they will call you back, talk through all the symptoms with you, and then tell you if they think your son can wait for a regular office visit. The doc will be looking for specific things in your answers to indicate to him/her if this is a viral or a bacterial infection (swollen glands, rash, mucous color, obvious pain, etc.). If they feel it may be bacterial, they will tell you to go the ER or a walk-in/urgent care clinic. Even if the doc says that you don't need to be seen, always follow your "maternal instincts". I have found that mothers are usually right. Some docs pay more attention to this than others. If you just feel that he needs to be seen, then go. It will make you feel better, and it may make him feel better. In the end, you may get there, wait for hours, and be told it's a virus and keep doing what you are doing. But you will KNOW that it's not bacterial and doesn't need a prescription and that you are doing the right thing.
Probably the one thing I can't help you on is the thrush. None of my kids had it. But I do know that what others have stated here is accurate. It is a white coating on the tongue, caused by a yeast infection, normally only in breastfed babies. There are ways that other kids can get it, but that doesn't happen very often. So, if your son doesn't have a white coating on his tongue, I think you are ok.
From what you wrote, it sounds as though your son just has a virus and will be ok in a few days. But if he shows any other symptoms (tugging his ear, green mucous, swollen glands, rash), please be sure to get him seen.
Best of luck! Happy New Year!
T.