Some loneliness is other people not reaching out. Some of it is you not reaching out. Check which.

Being on the outside can happen for reasons that have nothing to do with you, and it happens to people who are easy to like. It can also happen when everyone in a group is waiting for somebody else to send the first message, which is more common than it sounds. Those two feel identical from inside, and they need completely different responses.

Look back a few weeks and count who you contacted first. If the answer is nobody, try one message with no occasion attached. If you have been reaching out and it keeps going nowhere, that is not your failure, and the energy may be better spent elsewhere.