Just rilex. The pain is NORMAL because you haven't you that muscle (to its limit). The pain will usually disappear within a week.

Leg day on PHAT is very painful. 4 days of pain but I like them. Now on Max-OT, the pain isn't as bad as on PHAT but 2 days guaranteed.

you mean during the routine or after few days of resting? During training, lactic acid buildup is the most common problem for the soreness while injury also a problem. If the sore from acid lactic, just rest for few minutes (if you are doing weight training, there is the rest period between each sets). That is when you recuperate and continue your workout afterwards.

Don't do stepmill or any other cardio after a leg day. It's not worth it.