A prominent bony bump at the posterior heel area, is often a combination of several pathology. The GP is right that it could be insertional Achilles tendinits. Sometimes there is additional calcific deposits in this region from the chronic inflammation, and that lead to pain and swelling as well.
A Haglund's deformity is a prominent calcaneal spur that abuts the Achilles tendon and causes pain. And finally, a retrocalcaneal bursitis can add on to the symptoms. This would be located between the Achilles tendon and the Haglund's deformity. Together, all three pathology is collectively known as Haglund's Syndrome.
It rarely goes away, especially if there is a calcaneal spur. As that is actually "additional bone", it won't disappear on its own. Achilles tendinitis or retrocalcaneal bursitis may settle down if treated properly. It would be important to visit an orthopaedic surgeon, and some investigations may be necessary to diagnose the problem and see how severe it is.
Treatment would then be tailored to the problem. This may be conservative, with medication and physiotherapy. Sometimes surgery may also be indicated, especially if the bump is a large one, and conservative treatment fails.
It is a very treatable problem, so I would advise you to seek a consultation soon, if it bothers you. Hope the above information is useful.
Best regards
Dr Sean Ng