I have a dark scar that changes shape sometimes it would be small as it would fade but then it becomes bigger. its dark brown and noticeable.

Hyperpigmented scar: A scar can get hyperpigmented in the first six months. It could have skin changes from excess sun that are a risk & need to be checked. But the ""fade" and then "bigger" as a cycle suggests that swelling from exercise is making it look bigger and that it looks smaller when you are at rest. The area of anatomy would be helpful to answer this question better. Photographs of the changes would help.