need help constipated baby.

Hello moms. My 9 week old daughter is constipated After the doctor changed her milk to soy milk. After being allergic to enfamil milk. It is breaking my heart to see her trying to push and nothing coming out. I tried prune juice. And even the old fashion way. A q-tip and Vaseline. To help her. Do you moms have any other advice to help her go. I trying to figure out if she to young for a suppority. And also calling the doctor Tommorrow