Cracks in fiberglass pool

I currently have 3 cracks in my 10 yr old fiberglass pool.

They are at different parts of the pool. 2 of the cracks are about 15' apart from each other. They start under the tiles around top edge and extend down about 18" the other crack is on the opposite side of the pool it starts under the tiles and extends down about 3'.

I have used 2 part pool putty for a temporary fix, but need to do some fiberglass repair before the season starts. My question is 2 part. Whats the best way to fix the cracks, best materials etc. and what could be the cause. I understand most fiberglass cracks begin due to external water. The strange thing is before the cracks I never lost much water. There are no underground water lines in the area. My pool is 38' X 18' and is 8' deep. I live in Louisiana

Thanks for any help.