Transitioning to formula..

How do you go about transitioning to formula from breast milk? My baby is almost 3 weeks but I have been feeling so overwhelmed and feel like I have no time for my 3 year old since I feel like I’m constantly nursing.. I wanted to breastfeed so bad but at this point I just feel so overwhelmed and anxious with it and am seriously considering switching to formula. I just need some advice.. I feel so guilty😭