What sickness do I have?

Could just be a common cold. I doubt it's anything worse than that because you don't have a fever or anything--so luckily and hopefully it remains that way! I too have a very low body temp, the same as yours actually, but there's really no reason to worry unless it starts getting into the 100s. I just had the most terrible virus, temp was up to 104 which relative to other people is like 106ish D: So there's no need to be alarmed about that at least, it could've just gone up from walking around, doing everyday things, coughing, etc...