Here's the fucking secret motherfuckers: PROGRESSION!!! There is research that shows clearly that the load is the prime factor in hypertrophy. PRIME factor! Not the only factor but the most important factor.
Forget about failure, DOMS, and everything else... do a routine that allows you to increase loads over time using a reasonable volume.
If you have been training with the same loads for the past 3 years you most likely haven't grown, unless you added a bunch drugs.