I don’t doubt that you have a sincerely held belief that you are trapped in a time loop, but I’m highly skeptical that such a phenomena is physically possible. That would leave me to conclude that the most likely explanation would be that your mind is experiencing things that are different from physical reality. We know this is something that is possible. People who have had their stomachs surgically removed still experience hunger pains. Amputees experience phantom limb pain. Optical illusions are a way that all humans can experience the ‘seams in the matrix of reality” that our minds create. We know mental illnesses (and other things too such as psychoactive substances) can cause delusions and hallucinations that are not malingering deceptions, but sincerely held beliefs.
So my best guess/advice is your belief is likely a mental phenomena, but I’m certainly not qualified to venture a guess as to the mechanism that’s producing it, and it would be reckless to offer an opinion on an actual medical diagnosis. The best person to discuss this with would be your therapist, and if that’s been unsuccessful, I think getting a second or third opinion from another licensed mental health professional would be the best course of action. Wishing you the very best.