I exercise 4 times a week (High intensity cardio), follow a strict diet and take my Eltroxin on time everyday, however I still cannot loose the weigh?

Wt. It depends on what your strict diet means. You may still not be eating the right food . You need to see a dietitian and be followed to make sure you comply . It's an absolute fact that if you eat less calories than your body uses you will lose wt.
Hypothyroid. Many times this occurs when the etiology of the weight gain is actually thyroid related and not so much the amount you exercise or consume, You should get a Thyroid Hormone level tested by a blood test.