Are you sure that it's not because of what you are eating?
When my cholesterol levels were high, I decided to become a vegetarian and try and lower them. However in my early days as a veggie I basically supplemented my diet on things like potato's. All the extra starch caused my triglycerides to go through the roof! So it might be something that you are unaware of that's secretly doing more harm then good.
However if it's not that and you are sure, it could be based on your gene make up. High cholesterol
can be hereditary in which case you should consider going on some meds to help reduce it. Check with your Dr.s and your RN to see what you could still be doing to help bring them down on your own.
Best of Luck!