I'm pretty new to D&D and have a question. I am currently playing as a rogue swashbuckler (lvl 3) which encourages dual wielding. I love this mechanic and enjoy playing it so far but I'm confused about the bonus action part of it. I understand you don't add bonuses in most circumstances to the off-hand attack (sneak attack being an exception).
However, my DM tells me whenever I attack with my offhand I need to roll twice and take the lower of the two because I have a disadvantage with my offhand (which is also my bonus action). I can't find anything that says I need to do this. If this is how it works? Is there any way I can get rid of having a disadvantage with my off-hand? Or is this just a DM choice?