Have bitten by bed bugs all over and now I have these darker marks, how can I get rid off these they make look dirty, I have heard of monobenzone would it work, the marks on my neck, torso, arms, legs

You're positive these marks were caused by bedbugs? I know they can cause an allergic reaction and red bumps, but I've never heard of black bumps.

They are red bump in the beginning and when it is not itchy any more I am left with darker mark
Because I scratch them a lot without knowing these are bed bugs and you should never scratch

Try fade creams like licorice or bleaching cream