How to encourage milk supply?!

[Maybear]

So I have been breastfeeding for 7 weeks now but only from my left boob as he only preferred that from birth. I have been expressing my other boob but got a bit lazy (missing days) with it and now I'm uneven!
This has now lowered my milk supply, down to about 20ml. I have managed to get him to take to it now but the supply hasn't picked up currently been trying for 4 days now and no luck
Is there any way I can increase my milk supply in that boob? Any suggestions as I am walking round lopsided?!

What you express doesn't bare any resemblance to what a baby will get when they feed. Just feed from both sides and they'll even up.

Only thing, I think, that will increase supply in one boob over another is feeding more from that side. Mine were always a bit uneven with DD having a preference for my left side from birth