Swelling and pain in the back of the right foot, the specific causes are as follows: 1, deep vein thrombosis in the lower limbs: When thrombosis occurs, the blood return to the lower limbs is blocked, and a large amount of blood may accumulate in the foot and lower leg, so there will be edema, swelling of the back of the foot and swelling of the lower leg, which will be accompanied by continuous pain in the lower limbs in addition to swelling. 2, lymphedema: This is mainly due to the blockage of the lymphatic vessels in the lower limbs, causing the accumulation of lymphatic fluid in the lower limbs 3. Soft tissue injury of the back of the foot: especially if there is a sprain of the back of the foot after sports, or if there is a chronic strain of the back of the foot, the local soft tissues will exude more tissue fluid, which is manifested as swelling of the back of the foot.