Hadn't had sex with bf for 1 month until yesterday and it was painful and sore for me, tried again today, still painful, lost virginity 4 months ago?

Painful sex: By any chance have you tried different positions? Another issue may be the amount or lack of foreplay - to allow your body to produce vaginal secretions allowing penetration. Were you relaxed this time? all of this will change how your body reacts to a sexual stimulus. Girl on top allows you to control penetration. I would try some lube and make sure you have plenty of foreplay first.