I am 35 I never had trouble with high pressuer until I had a blood transfusion 3years ago could this be part of my high blood pressure

No, unless you stay worried about the blood pressure.

You may ( unless you check it all the time) have had high blood pressure for years and never know it.

Stress, job chages, moves, medical issues can all cause it.

No it has nothing to do with blood transfusion.

There are many many factors and things that can cause problems with blood pressure as long as it is being monitored and or treated and your doing things to try to keep it down.

I know it is normal to look for a cause, but a lot of it has to do with Food/Family history/Lifestyle in general. Stress and anxiety can be a contributor as well.