Adderall Increases when how much?

I've been on Adderall for almost 2 months. The regular kind no the XR. The first month I started with 10 mgs in am and 5 mgs in afternoon. I'm now on 12 mgs in am 7 mgs in the afternoon. It takes a few cups of coffee to get that morning one going I'm wonder if I should ask the dr to increase to 15mg in the morning and 10mg in the afternoon as I'm finding it a little hard to get through my work day. Is it normal to need to increase so soon? Any thoughts on this would help.