Switching to formula from breast milk 5 months old!

So I’ve been exclusively pumping and feeding my baby only breast milk since she was born. She will be 5 months on the first. I’m going to stop breastfeeding and move over to formula due to a lot of personal issues I’m having myself and cannot take the meds I need while breastfeeding. I tried to stick it out for as long as I could, but I’m in so much pain, going through so much depression it’s ended up causing me and my SO to break up over how bad it has gotten. I work 60+ hours a week as a third shifter & am so exhausted as well which keeps me stressed trying to find time to pump on top of the bigger issues. I feel like I’m letting her down, but am starting to think it’s not worth me feeling the way I do. How should I go about switching her?