This is my personal bias, but I *hate* Mexico. My advice would be to find a nice all-inclusive resort, and just relax on the beach and drink for a week.
Que Pasa? Isn't Punta Cana in the Dominican Republic?
EDIT: Stupid long post... i shoulda known someone would beat me to it.
I was in the DR for 9 days with my girlfriend a year and a half ago. I loved it there. We stayed in Sosua, which is just east of Puerto Plata. We didn't make it to Punta Cana, but if you are open to staying elsewhere and just being in Punta Cana for a wedding, I know a great bed and breakfast in Sosua. Probably the best place i've ever stayed at, run by two british ex-pats.
I would say there is enough to keep you occupied for a week. Things to do:
Cable car ride up the mountain in Puerto Plata - Incredible views and there is a smaller version of the Jesus Christ statue on top like in Brazil
Go kite surfing or windsurfing in Cabarete. Its the capital of North America for those sports.
Take a day-trip via a tour group to Paradise Island. Its a small sand bar surrounded by a corral reef. There's drink stands on the island and you go snorkling amongst all the tropical fish.
Playa Rincon - Closer to Punta Cana than to Puerto Plata. We made the drive all the way out there and i'd have to say its one of the nicest beaches i've ever been to. Kinda hard to get to (rental car almost didn't make it due to the rocky road) but so worth it. White sandy beach backed by palm tree forest that stretches for 4.5km. Oh yeah, and its usually deserted.
Anyway... the DR was one of my favourite vacations... so relaxing... and lots to see. If you're feeling adventurous, take a guided tour into Haiti... they generally use bullet-proof busses with armed guards.
If you've got any more questions, shoot me a pm.