My 9 month old son had to get a cast

My heart is broken I’m so confused don’t know when and where it happened I just knew last night something was off when I changed his clothes. Took him to the ER and what I thought was nursemaid’s elbow was a small fracture on his forearm. Dr said it’s more common than I would think but still he wasn’t acting too much different and there were no abnormal Serious cries or episodes that had me concerned. Spent all morning and evening at the hospital he’s drained I feel so bad my baby ....