How can I lighten a dark stomach, butt and back years after having a baby? Any laser treatments available? (Photo)

It’s been seven years since last pregnant and my stomach, back and butt is at least four shades darker than the rest of my body. What treatment can even out my skin tone? I’ve never been treated for this however I’ve tried hydroquinone to no avail. Please keep in mind that my stomach was dark well before pregnancy and became darker and stayed this was well after. I’m willing to do anything to correct this! Thanks in advance!