Mri found 17mm pineal cyst, have headaches,nausea,tingling. neuro said repeat scan in 6 months. should i be worried?

Depends: The fact that you have symptoms is concerning. A pineal cyst is benign but can become large and cause symptoms like the ones you are having. Waiting 6 months for repeat imaging is a reasonable plan to see if it is enlarging.

Second Opinion: You could get a second opinion, which I guess is what I am on some level! ;-) If it is just a cyst, then a wait and approach attitude seems fine. There are three things that will happen during the 6 months: 1. It will get bigger 2. It will get smaller 3. It will stay the same size. You could see a neurosurgeon, but that's moving towards a surgical approach to something that might go away.