Hello, i am not new to this forum, i have been browsing around for quite a few months. I am 16, 5.10 and about 140pounds. Iv been lifting weights on and off for the past 4 months. 3 of those 4 months were really good. i worked hard, saw size gains and overall felt great. At the end of those 3 months though, my benching began to gave me some trouble. After i finished benching, my lower back would have a tense feeling. Is this normal? i heard lifting your legs onto the edge of the bench at an angle helps because it straightens your back, but it doesnt seem to work for me. Because of this i stopped benching and i want to start it again, without the pain.

Are there any warmups, exercises or stretches i can do to prevent this? or should i change my benching technique?

Thank you