Milan have done a really good job by taking advantage of Juventus' bad form recently. They are at the second position now after this. I find their productivity quite decent this season compared to their nearest opponents like Juventus and Bologna. The main problem is more related to Milan's defending. They have conceded 33 goals in 29 games. 

They can actually solve this problem by transferring better defenders this summer. They spent 100 million+ euros in total for transfers last summer if I'm not wrong. They should focus on their defense line more next time they make transfers. If they conceded much less goals than this now they could have been in the title race.