Hmm, that doesn’t seem right. If you described your symptoms as “tired, aches, headache, dizzy, brain fog”….I would say “yes, that’s all typical of beginning fasting again.”
But running a temperature is not. Keep an eye on that.
IF on its own shouldn’t cause a fever. Nausea, sometimes, but not a high fever.
If you want to continue IF without seeing a doctor, then you need to eliminate variables. Like cut out exercise for a day or two and see what happens. Or change your first meal. Move your eating window. See if one thing in particular is causing the issue.