plateaued at 280lbs
 

Looking for a little advice on what I might be doing wrong.
First of I am 36 male and 220lbs, been lifting weights now for roughly 9 months.
I work all parts of the body legs all the way up and do 4 serious sessions every week without fail. I recognised when I switched up my training to not only heavy weight but focusing on lighter weights at high reps I really noticed a difference, I also noticed a difference especially in recovery when I started taking protein supplements about 5 months ago.
My problem is for 6 weeks I have plateaued at 280lbs, for the life of me I cannot burst that mark.

I do run once/twice per week and someone has suggested this might be an issue, any help would be welcomed.

Mark Leroy, Ayrshire OH