So I'm not exactly new to home brewing as the batch in question is #15 and #5 all grain. The recipe is question is a cream stout AG kit from Midwest Supplies. Brew day seemed to go well and hit OG spot on at 1.044. Fermentation started as expected and within 24 hours and a beautiful krausen had formed. Krausen fell after about 3 days as usual and then left it to condition for about 18 more days. Fast forward three weeks and on bottling day the FG reading is only 1.020 (target 1.010) giving me a approx abv of only 2.63 when it should have been around 4.3. I have missed OG before by small amounts but FG usually came out near where it should. Does the addition of lactose in a cream stout effect these numbers? Sorry for the newbie like questions but I've never really understood the science behind brewing as much as I should. Any info on where I may have gone wrong would be greatly appreciated.