Why does one develop swelling after snake bite?

Hi doctor,

I am a 40 year old female. I got cottonmouth bite on the back of the left and right ankle. Three people saw and confirmed that as cottonmouth. I do not believe much venom was released. It happened under shallow water. I got immediate pain as if repeatedly the ankle and feet got hit with a bat and a burning swelling began quickly. I went to the ER. They monitored my blood for two hours and decided no antivenom. I was not given either a tetanus shot or any antibiotics. From the laboratory work, they said everything looks good, but I could not stand or walk. They sent me home with Ultram and Ibuprofen 800 mg. After two days, the swelling slightly increased instead of going down. My fiancé took me to different hospitals. The swelling and the fang marks were evident. Again, the laboratory results were normal. I was still in pain and swollen ankles. They gave steroid intra muscular (IM) injection and Prednisone pack and suggested antihistamine. It has been six days. Still, I cannot stand, walk or care for myself in any way. The swelling has not got down. I have kept it elevated and put some cool fabric packs on swollen areas. It seems to help with burning sensation. I have been drinking Echinacea tea, water and taking all medicines prescribed such as Ultram, Benadryl, Prednisone and Ibuprofen 800 mg. Back of my legs up to the thigh is swollen, entire legs hurt and tender to even minimal touch. Bruising has darkened and the swelling has not gone down. There are no red lines and no skin rotting. What shall I do now? I want the swelling to get relieved. I am scared. How to reduce the swelling? Please tell me what I need to do just to be able to stand briefly. The pain has subsided from 10 to 5, but if I try to stand by just keeping the foot down towards the floor, then the pain is excruciating. Please help.