helloo bev! tailbone pain or abrasions could be due to the following causes: 1) the floor is too hard - try using a thicker/softer exercise mat, or place something soft under your hip. Or, try doing your sit ups on soft ground usually found at those exercise stations. Those blue/red grainy rubber bits thingy. I usually do mine there after a run. 2) improper posture/way of doing. The more reps you do, the more tired you'll be, resulting in you using your lower back and hips to bring yourself up. In doing so, your lower back will be on and off the ground, and when it lands, your tailbone will absorb most of the impact, resulting in pain. So, try decreasing the amount of reps for each set, instead of 20, try 15. And perhaps increase the number of sets, if you feel no kick. Hope it helped! :)