You are not using proper form, or the floor is simply too hard.
Use more padding and tilt your hips in towards your belly button.
Sit-ups are hard to do perfectly correct, and may end in more harm. Other alternatives for ab-workouts would be better, like crunches.
same thing is happening to me, my mom is taking me to see a specialist.
The discomfort you feel in your tailbone while riding your bike may be due to the pressure and friction placed on that area from the bike seat. The design and positioning of the seat can cause strain on your tailbone, leading to discomfort or pain. Consider adjusting the seat height or angle, or investing in a seat with better cushioning to alleviate the pressure on your tailbone.
The tailbone is the end of the spine.
The coccyx is what we refer to as the tailbone.
He didn't do situps, silly!
The medical term meaning pertaining to the tailbone is coccygeal. The proper name for the tailbone is coccyx.
Coccyx is the scientific name for the tailbone. The jawbone is called the mandible in scientific terms.
Coccyx
50+ sit-ups a day for 2-3 weeks (your muscels might hurt the next day,but that's actually a good thing!!)
the cocyx is the tailbone
Coccyx
That would be the Coxyx - pronounced 'cocksix'