Hi, Thanks for using HCM.
Since your middle finger penetrates, and he has complete erection just get checked whether your hymen
is still there ar torn out. Since if hymen has more fibrous tissue and not torn then the chance of penetration will be difficult and check whether the length and strength of penis is sufficient to penetrate. If not there may be some problem in penis. You can conceive if semen is ejaculated in vagina. If unruptured hymen get a small surgery to cut it open and he can penetrate or if he has any problem show it to doctor once. Consult your doctor for examination and management.
Hope I answered your question. Feel free to ask me if you have any further queries.
Wish you good health. Take care.