hello! I am a little confused on how to achieve good breath support. should i be tightening the abdomen to keep it expanded? when i try to keep it expanded it causes pain in my abdomen and back. i think the lack of breath support is what's causing the stain in my voice. thank you!

Not tightening - we typically think of breath support as a gentle pushing "down and out" in your low abdomen. The goal is to engage your low abs and intercostal muscles so that your ribcage remains expanded when you sing. The best and gentlest way to train good breath support is on a lip trill: https://www.30daysinger.com/blog/lip-trills-all-about-the-vocal-exercise.