How does Sex work for us?

I recently turned the legal age in my country and I have been exploring sex even before that. Even after months of self pleasure and watching and reading tutorials on the internet I’ve never had an Orgasm. I want to experience it so badly. Sometimes while I’m playing with myself I can feel it building up, feel myself almost there but then it drops down into nothing and I have trouble building it up again. Sometimes I feel myself climaxing but then I feel the need to let go and I just can’t so it stops completely. Another concern for me is I don’t know how to properly stretch myself. I recently started using dildos and I have a hard time getting them in without pain at first. I know I’m not stretching properly but don’t know what I’m doing wrong. Aftercare is another thing, I know about peeing before and after and wiping/washing down there but that’s about it. Most of the time I use a dildo I get UTI after so I know I’m doing something wrong. Recently I used a dildo for my self pleasure after a long time without it (had UTI and yeast after and got scared of using it again) it was all pain at first and a bit of pleasure with pain so I stopped and tried to stretch myself. I finally reached just pure pleasure after pain for minutes but then I saw a bit of blood and got scared. I know I can probably Google this stuff but most of says I may have STD’S (I really think it’s impossible for me due to the circumstances) but it still got me scared so I wanted to ask real people. I also don’t have any other people in my life to ask, so please help me.