1 month and constipated... what to do?

My one month old strains and cries like she is trying to poop and often nothing comes out and she only poops like every 2 days (formula fed) and sometimes it is like tiny Hardish balls then goes to extra thick extra sticky peanut butter. How do I relieve this constipation? Do I need to change formulas? The constipation ease from mommysbliss is only for 6 mo and up...