Why do I slack?

I don't think I will every understand why I let myself get into these situations. Practically all summer I never stepped foot in a gym, never lifted a weight. I was doing training, but mostly swim, bike, run stuff, trying to figure out this whole triathlon thing.

Now trying to get back into the swing of things leaves me completely sore. I did legs on Wednesday and still today my legs and butt muscle are very tender. That coupled with I feel like I am lifting girly weights because I've lost so much strength really pisses me off. I know muscle has memory... I hope mine remembers quick :o)

Lat Pulldowns - 2 x 12 x 70
DB Incline Bench - 2 x 12 x 20
Seated Row - 2 x 12 x 75
DB Flat Fly - 2 x 12 x 15
Rear Lat Machine - 1 x 12 x 30 and 1 x 12 x 40
Side Lat Raise - 2 x 12 x 10

Then I did intervals on the Elliptical. Now to figure out what to eat...