Can a head CT scan (with and without contrast) radiation cause a brain tumor to grow and cause symptoms in 2 years and 8 months or 3 years? Possible?

Incredibly unlikely. The amount of radiation in a single head ct scan is extremely low.
Unknowable. Unfortunately, no one can definitively answer your question. Your question can be answered statistically (radiation from radiology procedures does cause a certain number of cancers if you study large numbers of people), but we can never say for sure exactly which cancer cases were caused by such radiation.