Is it normal for newborn na hindi mag poops in 2 days?

my 18 day old bby is currently on formula fed, last sunday pa huki nyang poops nung nag bf sya sakin. but since I need to take antibiotic di ako pwede magbf sa kanya and need sya iformula fed. Should I worry? anyone here who experienced the same? thank you in advance, momshies! #firstbaby #pleasehelp #firsttimemom