It might be possible that your scar was irritated by your bathing suit. If concerned. see your surgeon in person.
Thank you for your question and I am sorry to hear of your scar concerns. Without a photograph it is difficult to offer definite advice but there are treatment options to improve your scar pain/sensitivity as well as its appearance. Attached below is a link with useful information. I would recommend reaching out to your plastic surgeon for an in-person evaluation. Once the quality of your incision line is known then the appropriate treatment can be instituted. Hope this helps.
Stretching a scar can cause it to be irritated.
Have you doctor check it to see if the scar can be improved or revised.
At 10 months after surgery your scar is most likely hypertrophic or thickened as opposed to being a true keloid. This can happen for many reasons but can easily be corrected.
Scars continue to heal for approximately 1 year so you may still benefit by steroid injections and massage at this time. If this does not help settle the scar then a simple scar revision would be the next step.
I recommend seeing your surgeon for an examination.
Your scar is likely hypertropic and not a keloid. Thick or hypertrophic scars usually develop when there is a genetic predisposition and or undue tension on the scar. Treatment involves several options including injections with catabolic steroids and topical agents. It is best to check in with your surgeon to develop a treatment plan.
I am sorry to hear about the concerns you have after breast augmentation surgery. Sometimes, hypertrophic or keloid scarring can occur; these scars can be sensitive, sometimes without a specific "reason". Based on your description, it sounds like you may benefit from scar revision; hopefully the scar can be changed to a finer line and better placed between the areola and surrounding breast skin. Best wishes.
Generally a scar takes about a year to mature. The goal would be for the scar to be soft, flat, and blend. If a scar is becoming hypertrophic, there are some simple things your surgeon could recommend like scar creams, massage, or even steroid shots if it's particularly bad. If a scar has been pain-free until recently and suddenly becomes painful with a new piece of apparel it most likely the mechanical rubbing of the scar causing the problem. Changing to different clothing or adding extra padding may help.
You may have hypertrophic scarring. There are ways that your Plastic Surgeon can help treat this. I recommend that you speak with them and ask to be examined in person.
All the best