constipated baby i think

I think my baby who is 4 months 3 weeks is constipated as she didnt poop since last 3 days and is lot of gassy..the gases are pretty smelly and she tries really hard to get them out of her system! She is active, wetting usual amount of diapers, taking feeds regularly and also she is sleeping fine. She is being enf and i havent started solids yet... Any idea what is happening el contact the doctor soon