What's your air temperature? Are your lights set on for 14 hours?

If the temps are OK, and the lighting is on for 14 hours a day, see if there's a qualified reptile vet in your area that can get blood work to see if there's infection.

Most sliders don't develop eggs until they're 6-7" in shell length.

Katrina
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0.1 Iguana - Tiffel
1.2 Eastern Mud Turtles - Fred, Ethel, Edith
0.0.1 Giant Mex. Musk Turtle
Foster turtles: More than I'd like the husband to know about.