Ovulation can happen 36 hours after your positive OPK, so it would be completely normal to have O spotting now. Your midwife is wrong. Random mid cycle spotting happens to a lot of women and isn't strange.
However, it could be O spotting, it could be random spotting, it could be completely unrelated to your uterus and be the result of rough sex. We don't know and honestly can't tell you.