Cheryl, First, do you have a fever? Often 1st sign of an infection... Do you live in an area known for venomous spiders, (black widow, recluse, for example)? The dot in the middle is probably the puncture point where your skin was pierced. The, "fluid" is probably a build up of white cells, etc.trying to fight germs that the spider introduced into your body. Please, don't puncture or squeeze this as an attempt to rid the fluid. This could introduce harmful germs into your blood stream and cause septicemia,(blood poisoning).
Antibiotic ointments are not going to get to the source of the infection since you describe it as closed. No heat, no ice unless directed by your physician. Oral, or IV antibiotics are what your physician will prescribe depending on the severity of the infection.
Good luck, Cheryl. Please consult your physician as soon as you can. I hope you get well soon.