Going for the medicals without instruction, if I remember well, from the 2nd NL, would be a waste of your time and money. The Medical instructions specify where you should take your medicals from. So you cant just walk into any clinic and ask them to give you a full medical. The medical results are never handed to you in any case - they are sent directly to the US Embassy, so that there is no risk of tampering on the part of the applicant. So, all you can do is just wait and gather the documents detailed in the 1st NL, making sure that everything is in order. You wont have much time once that 2nd NL comes in.
Trust me, I know how killing the wait is for that 2nd NL. It builts enough doubt in your mind to make you want to give up, and I know one person who quit the whole process at this point, not knowing that it was only a matter of patience, considering he didnt have anything wrong with his supporting documents etc. Some people I guess wither under certain pressure.
It'll all be good, just wait a while longer.