is my baby ready to start on food?

She's 4 months. Every time I try to feed her, she doesn't seem to get a GOOD feeding except for at night. If I had her on food, I would think she was ready to wean off. 
But she's not on food. Just breast milk.
I feel like she's not getting enough. Is she ready for baby food? My plan was to wait until she was about 6 months old...