It is probably wind/gas https://www.healthline.com/health/gas-pain-in-chest#symptoms

Do not worry, unless you get more symptoms that, like difficulty breathing, I would not worry.

Drink plenty of water, there are a few herbal and OTC remedies below for you.

Natural remedies for gas include Peppermint tea. Chamomile tea. Anise.
...
Over-the-counter gas remedies include:

1. Pepto-Bismol.
2. Activated charcoal.
3. Simethicone.
4. Lactase enzyme (Lactaid or Dairy Ease)
5. Beano.

If you continue to get the pain each time you take Gabapentin going forward, I would schedule an appointment back with your GP to see your options.