Medical is required for I-485. So plan accordingly. Go to USCIS website, search for doctor or clinic. No need to get prior immunization records. If you have them, then your cost may be lowered. I didn't had any records. It cost me $206. Everything was pretty quick. It took me 1 week from making appointments to getting the certificate. If some clinic has longer wait time then call another clinic. Does not matter where you get the medical done as long as it is in USCIS list. Just go there, everything will be taken care of.