I had a similar problem with a honey blonde ale i made!! it was a partial mash that i created, but i found that i didn't soak the grains long enough so i didn't get a full starch conversion. my O.G. was 1.035 when it should have of been 1.050 according to beersmith. After the first week it was down to 1.005 so i added a pound of corn sugar(boiled with 3 cups of water) and it brought it back up to 1.015 and i checked it after 3 days and it was back down to 1.005, so my guess is that i got another 1% which brings it to about 4.9%abv. Flavor wise, it made it a bit drier in taste, but i said screw it and decided to dry hop it for awhile to just try it out! Good luck with your brew!