Your probably not doing HIT correctly,
HIT doesn't just target strength its the main foundation in size and mass,
It takes time to understand and train your body and also your mind to go to failure,
Take a lot longer than 3 months you wont be hitting failure yet let alone a proper HIT routine for 6 weeks,
You might not like HIt because its hard work, it takers a lot of mental training and serious mind control you may not be up for something so intense and other method might be for you but imho no other style create thickness, size and over head turning results than HIT,
Its also impossible to train HIT for 3 months without a pullback, its indicates your not training pure HIT.
Move on to easier routines and get mediocre but remember not everyone is the same and you may respond better to volume who knows but without giving some 100% you have no idea but I have to ask the question I really suspect you cant give HIT 100% what is needed to change the body into something special,