I have recently been diagnosed with a high triglyceride level but why is my total cholesterol level normal?

Different lipids: Triglycerides contain mostly fatty acids linked to glycerine and have little cholesterol in them. Cholesterol is not the only harmful lipid. High triglycerides can cause skin lesions and more seriously, precipitate acute pancreatitis. Reduce caloric intake, carbohydrates and lipids, take fish oil and see your doctor.

Possible.: The formula for calculating total cholesterol is tc=ldl + HDL + trig/5. It is possible to have high trig and not have tc elevated. It is clear based on your normal tc level that your trig are not elevated much. Serious trig elevations are levels above the 500-1000 mg/dl range.

Independent control: Blood fat levels can be linked since their metabolic pathways are often intertwined. However, their manufacture & degradation can be separated such that cholesterol and triglyceride levels can & do vary independently. That's also why treatments effective for one type of blood fat may have little effect on other types. Triglycerides tend to be responsive to lifestyle changes more than other fats.