Insurance Is Lowballing My Car Accident Claim And Demanding I Sign A Full Release. Do I Have To Accept This

Location: Ohio, USA. About 4 months ago I was in a car accident that was clearly not my fault. I was stopped at a red light, other driver was texting, never hit his brakes and slammed straight into the back of my car. Police came, he admitted he was looking at his phone, the report lists him as at fault and he got a citation. I went through his insurance because I only carry liability on my old car. At first things seemed straightforward. They paid for a rental for about a week and sent me to one of their "preferred" body shops. The shop looked at the car, said the frame was bent and some stuff under the hood was damaged, and pretty quickly declared it a total loss. The adjuster called and offered me what honestly felt like a low number for the value of my car. I pushed back a little, sent them listings for similar cars in my area that were going for more, and the adjuster grudgingly bumped it up by like 600 dollars and basically said that was the final offer. Around the same time my neck and back started hurting more. I went to urgent care the next day after the crash where they said it was probably whiplash and to rest and take over the counter meds, but the pain did not totally go away. I have since had a couple of follow up visits and some physical therapy that my own health insurance has been covering with copays.

Now the other driver's insurance has mailed me a packet that is freaking me out. It includes a check for the car amount plus a small extra amount that they say is for "inconvenience and minor injury", and a long legal looking form called a "full and final release of all claims". The letter from the adjuster says that once I cash the check and sign the release, the claim will be closed forever and I "will not be able to pursue further compensation of any kind". The problem is I honestly do not know yet if my body is really OK. Most days I am just stiff and sore but once in a while my back spasms hard enough that I have to lie down. My physical therapist said if it doesnt improve in the next month I might need imaging or a specialist. I called the adjuster and asked if we could just settle the property damage now and leave the medical part open, and she said no, they only do one settlement and that if I keep waiting I risk "jeopardizing my chances of any payment at all". She also pressured me on the phone saying that juries dont award much for soft tissue injuries and I should be "realistic". I dont have money to hire some huge lawyer, but I also really do not like the idea of signing away my rights while I am still in pain. Am I actually required to sign this release or cash their check. Can I tell them to just pay the car portion and still have future medical claims open. Is it true they can just close the file if I dont accept in some time limit they choose. At what point should I be looking for an attorney and is it normal that they are trying so hard to get me to sign when things still feel up in the air with my health.