Lymph node problems? Anyone got an idea?!

Have a doctor palpate those areas to look for tender enlarged nodes and any associated regional inflammations.

I know when you have tight muscles in the lower back they can press onto the nerves going to the legs to cause pains in them. I would guess it could also be causing the pain in your groin so I would say freeing up your back muscles should help get rid of that pain and here's how to free up your back muscles:
Back:
(do from a sitting position)
Place your left hand on your left leg next to your body. Place your right hand over your left shoulder, fingers over the back and the palm in the front and firmly pull down on them and hold. After 30 seconds slowly lower your body forward and to the outside of your left leg, keeping your left arm fairly straight as you do. When you reach your lap remain there for another 10 seconds, release the pressure but rest there for another 30 seconds. Then reverse your hand positions and do your right side.
The neck ones are from tight muscles in your neck, nothing to do with nodes at all. When the neck muscles spasm out they are going to be pains there. To get rid of them you have to free up your neck muscles and here's how to do that:
Neck
Put your hands alongside your head so your thumbs are on the front of the muscle under your ear and your fingers are on the back of the muscle behind your neck. Squeeze your thumb and fingers together and hold. Relax your body. When your fingers and thumb touch, about two minutes, slowly lower your head as far as you can, release the pressure but hold your neck lowered for another 30 seconds.
For best results relax your body first by taking a deep breath and exhaling then remain this relaxed.