I have screws and plates in my right ankle and I feel something on top of foot that may be a screw or bone fragment I had the surgery last october. Is it possible that it could be a screw? It hurts and aches. It only got worse yesterday when I twisted it.

Very possible. It's not all that uncommon to get painful hardware which if you feel something hard right under the skin it could be that and fairly simple to see on x-ray so see your surgeon. Other possibility is nerve entrapment.
Yes. It's possible it's the screw. After surgery, the post operative recovery can take longer than people realize and everyone heals at different rates. Sometimes, the swelling decreases to the point where the screw can be prominent. Sometimes, the screws can back out. In any case, go back to your treating surgeon and present this problem to them. Hope this helps and good luck.
Painful hardware. It can be painful hardware or other conditions. Can be a sprain as well please consult a specialist.
Surely possible. See your surgeon for x-rays. If its a screw, easy for your surgeon to remove.
Without . Without examining you, it's difficult to say exactly what it is, but a loosening screw is a possibility if there was one placed in that area at the time of surgery. It could also be a tendon injury, bony abnormality, or a nerve sheath problem such as a ganglion cyst. Since it's getting worse instead of better, the best thing you can do is see your doctor or your orthopedic surgeon for an exam. They will also have the records from your surgery and will know for sure whether it is a screw or not. In the meantime, follow the "rice" therapy (rest, ice, compression and elevation) and try Ibuprofen for pain relief until your appointment unless you doctor has different instructions.
Screws. As stated , it is certainly possible. Always consult your surgeon for any concerns.
It is possible. On occasion screws may back out. You may need to get an xray to check to see if it is the screw or the bone.