It's not at all unusual for you to be feeling aroused more, or noticing that you're more sensitive where you have bottom growth having started on T.
Honestly, what you're describing sounds like what plenty of people, trans or not, experience when they first start to masturbate. This feels good => no I'm done and it's way too sensitive now. Learning to build intensity in ways that feel good can take time! Try experimenting with building sensation more gradually - perhaps focusing on other parts of your body or touching your dick indirectly or through clothes and building up - and de-escalating briefly when it starts feeling too intense. Does that make sense?
Partnered sex brings in a whole lot of additional factors which can up the pleasure you're feeling, so while there is no one way that sex is supposed to feel, if you follow what feels good I don't see any reason why sex - partnered or solo - shouldn't be satisfying in the long run. When it comes to "finishing", for some people orgasm happens easily from the beginning but some of us have to learn how through some attention and experimentation. Think of clenching and feeling of "I'm done" as the seeds of an orgasm that you can nurture and grow. What do you think?
You also flagged a privacy worry. We have a bunch of tips in these articles about finding privacy and managing some of those anxieties:Deep Cover: Tips for Managing Anxiety or Privacy Worries When Masturbating at HomeHow can I masturbate without my parents knowing?