How can I make friends as soon as possible?

Im 28 and have always been seen as very very quiet. Im an introvert which doesnt help, never had a boyfriend and Im sick of having no friends to go out with. People on facebook have all kept the friends from school but I only had like 1 or 2 friends at school. Ive tried messaging people who I used to go to school with but they dont seem interested in meeting up. Ive never had a social circle and its even harder now because people I do know (through sports clubs etc) are married with kids. Just wanted advice. Im not too bothered that Im still single even though Id like a bf but Im not going to get one sat at home. Thing is I have no one to go out with and NO girl/woman that I know goes to a pub at night on her own. Ive been wanting t change all my life but I just never have friends to go out with. I go to the sports club with a woman (I give her lifts there and back) but she rarely wants to go out as shes married with kids. I might want kids sometime in the future but I dont know how the hell im going to marry if Im not able to get a social life. Heres a question out of interest. If you were in my situation what would you do to make friends as quickly as possible?

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