I think I have pregnancy brain - but could I have a brain tumor?

Doubt it. Talk to your doctor about your symptoms and what makes you memory better and worse! hang in there! i like to blame pregnancy brain for some of the things i do, but...
Less likely. Common things happen commonly. It is a fact that pregnancy brain is way more common than a brain tumor. Poor concentration, forgetfulness are common to happen during pregnancy. For that reason probably all are related to your pregnancy.However, if you are very concern or you do have other symptoms like-headaches, gait imbalance, limb weakness, slurred speech etc-you should talk to your doctor.