What could be the underlying cause of a chronically lower basal body temp?

When i run a fever – I hit about 36.8.

I sweat whenever i go above 36 degrees and for me that feels normal (35.8-36.2)

It has always been noted since i was young that my temperature was lower but now with crohns disease i run a constant low gradefever for me and it still doesnt cause my temp to reach what most doctors consider “high”.

I have had an infection lately and been extremely feverish and despite telling the GP that my temp is always low and that the 36.9 reading today was massvely high for me he just said no its not high so you arent really fighting an infection or anything.

Obviously low thyroid is one cause – my throid levels are within range (i take thryoid replacement but the low temp had been there before any thryoid problems)

Aso how is it possible to be sweating and fevery with such a low temp and are there any other problems this may cause?