I think you should call the doctor. Pressure sores are very difficult to care for by yourself. Joe had one at the base of his spine and because he could only be in a couple of positions, it actually never healed. I got him a wheelchair cushion made to prevent pressure sores, but that didn't help very much. We had visiting nurses to come and assess the problem and give us whatever they had to care for it, I changed the dressing several times per day, and kept the wound clean, but the constant sitting on it is what made it so difficult.
It got better for a while, then started deteriorating again.
The only way to get rid of them is to keep the wound clean and stay off the sore as much as possible. Walk as much as you can because exercise which promotes blood circulation helps.
They are caused when bloodflow to the area is not normal because of "pressure".
Donut shaped cushions are not recommended because they exert even more pressure.
We tried everything, Tegaderm, other special wound care dressings, special barrier creams, you name it. The nurse brought the special dressings she had available. These dressing are very expensive too.
So, get early intervention for your sore, don't let it get ahead of you, and I hope you have someone who can clean and change your dressings frequently. If it is on your backside, that is impossible for you to do alone.
I wish you good luck with it.
And for everyone who is having mobility issues, I hope you have someone who can view the back of you in the "sit down area" to look for skin signs indicating possible breakdown of skin, redness, etc.
There is quite a bit of information on Google for pressure sores, and even images. Take some time to look through them.