Implant Pain Caused by Retainer, Is Something Wrong with the Implant?

There is probably some residual swelling from the implant surgery, and the retainer is pressing on it too much. Bring your retainer into your dentist and show him.

Something is wrong. See yor dentist or orthodontist asap and keep the retainer out until you do. The most likely reason is that the retainer tooth is putting too much pressure on the implant and needs to be reduced underneath. The retainer was likely made from a mouth mould taken before the implant was placed.