I had a red bump, looked like a red pimple, where the shaft of my penis meets the pubis area for ~ a month. Today it was puss-filled, ingrown hair?

Good possibility . Inflamed or infected hair follicles in that region not uncommon and usually resolve on their own with good hygiene, warm compresses, and elimination of any undergarments that may be irritating that area. If persists, worsens, or accompanied by other lesions, recommend evaluation.