A: This is clearly a deep topic, but our first guess: It sounds like you need to carve out a space for the vocals to sit in, in the midst of all those big instruments. There are a couple of things you can try:
2. Take a look at your panning. Can you position some instruments that are obscuring the vocals off to the sides, creating a hole in the center of the mix for the singer to reside in?
3. Consider re-building your mix from the ground up (literally), beginning with the vocals, kick drum, and bass, then bring the rest of the instruments in around that core.