maybe it was too many reps. i know it sounds dumb becuase it was only a 3lb weight. when someone hits u lightley in one spot it dosent hurt the 1st time now after doing it a bunch of times it starts to hurt alot so lifting a light weight many many times it feels like lifting something heaiver and heavier the more you progress my advice is use heavier weights and do fewer reps. since you2’re a girl no im not being sexist im just saying what most girls ive seen do is use like a 10-15lb weight and do maybe between 10 and 20 reps take a break then do it again and do like 3-5 sets.
