I have a lump about a centimeter in diameter exactly where my leg meets the groin on the left side. it is tender. pimple feeling?

Cyst or abscess: This sounds like an inflamed cyst or an abscess. A cyst is a plugged hair follicle that gets filled with keratin (dead skin) debris. This can enlarge and become inflamed/infected. An abscess is a collection of pus, usually from an infection. They commonly occur in areas of friction (like the groin). I recommend evaluation by a dermatologist in case you require drainage or antibiotics.