Lungs are clear (ct scan) heart is okay (echocardiogram, ekg) then why oxygen saturation levels are low?

Possibilities...: There are many possible disorders that could have these test results. You should have pulmonary function tests since a ct scan does not tell anything about the function of the pulmonary system; only that the lungs look ok. Musculoskeletal disorders can have test results as you describe. You likely need to see a lung specialist to do a work-up and find out why your pulse ox is low.