My mother isn't happy for me

Why don't you just ask her if there is some kind of a problem? Does she approve of your fiancé? Is she mad he didn't ask for a blessing and acting out? Does she think you're too young or not in a good position to be married?

Agreed, time to take her out for a coffee and ask for some feedback, particularly if you have a good relationship.

Ultimately if the answer isn't favorable and for whatever reason she isn't happy, then my best advice is to keep the planning talk to a bare minimum. If she's not interested or displeased, you're only going to have a more difficult time making decisions and getting the input you need. If she changes her tune and starts asking about the wedding, feel free to open the door a little bit.

But trust me when I say, sometimes even the closest loved ones can be an unnecessary source of stress in your bride era. They will disappoint and upset you in unexpected, usually unintentional ways. Sometimes you have to cut your losses and welcome them into the process gingerly, and in a limited way. Good luck, and congratulations to you!