Pimple Under Eye? (photo)

The area that you have highlighted with the two arrows demonstrates prolapsed orbital fat. That is the fat that should be around and behind the eye, but as we age, slowly pooches forward into the eyelids.

You are correct in that occasionally, that area may also become more swollen. That could occur for many reasons [increased salt intake, too much or too little sleep, and a few other medical reasons]. The only way to differentiate between fat and swelling would be to get an in person consultation. An Oculoplastics surgeon would be a good specialist to see for this problem. [see link below]

The "pimples" are unrelated.

The swelling and pimple that you are describing may be related to the tear duct, which is in that area. I would go and see your doctor right away to make sure it is not infected. I would not pop it. Sometimes this requires oral antibiotics and sometimes it requires flushing the tear drainage system. If you have a dermatologist or oculoplastic surgeon, they would be the best for this problem.