Hi, my dd has this problem after she has had a virus. The paediatrician has told us several times, that in response to a virus the body can overheat or undercool and that it is quite common (apparently especially in younger children, my dd is now 4.5 but has this since birth) that they undercool. He told us that once below 36 degrees celsius we have to give her some food to warm her up (chocolate, crisps, anything she takes and quickly absorbs), luke warm chamomile tea/milk/etc, and warm her up with our own bodyheat (taking in our arms, blanket over her), to give her the food/drink we sit her up but sometimes she is in kind of trance like state. For us it has been very frightening, as she on occasions has become confused, shaking. Our Paed stresses key is too warm her up and not to ignore it! We use Braun ear thermometer (we have two and had it compared with paed and know that ours work fine). Anyway, not sure if this is any help with you. Also, calpol can lower fever, but it is not that if you don't have fever and take calpol you undercool, that is not how it works! Hope goes better soon.
I'm a bit worried now - ds2 has always been cooler than my older 2. They have normal temps of 36.4 ish. He has never really been above 36 as far as I am aware (and I do take temp readings quite often). In fact, on the night he was born, the midwife wouldn't leave (born at home) until he was warming up because he was a bit chilly. Ended up wrapped up in multiple layers, a blanket and under the duvet with me.
I have tried the calpol digital ear thermometer and the braun thermoscan one, and the readings are pretty similar.
Sometimes if a child has a high temp and given calpol after an hour or so they sweat profusely and the sweat cools the skin. If you have done the appropriate thing and removed clothing/bedding the child can actually get a bit hypothermic. In itself the temperature is not the worrying thing its how the child is. Drowsy, confused, after proper waking would be very worrying. Feeling cool to the touch? If warming doesnt work fairly rapidly as dikker advises I would get immediate help, as children who are very very ill will go hypothermic in the extremeties but very hot in their 'core'.
I would def wake DS to assess him for confusion and keep a very sharp eye on him.
Can you give him some food and take temp about 30 mins later to see if it increases (quickly absorbed food, chocolate ideally and maybe luke warm drink)? Problem with my dd is that she tends to get cold sweats after a virus, so bed is absolutely drenched, pyjama soaking wet (I change her pyjamas and bedding sometimes five times in a night, when we go through such a period) and her hair tends to be wet as well (dry with towels). But after chocolate, crisps (got some salt, as they lose salt with sweats), her temperature tends to increase quite quickly to more normal. However, she might have another spell like that a few hours later (I find it very stressful and exhausting, but we have had this since her birth). GP thought that it is kind of diabetes, but paed is adamant that it is in response to a virus and that it happens much more than people think but that a lot of people don't even realise because according to him they only check temp when child feels hot ... Does your son gets confused/crying/listless when he is cold?