I have heard that people can go through phases. As a transgender female how will I know when my being a transgender female outlasts the "being just a phase" category?
How long have you felt like this? If it is a long while, then it's probably not a phase. Just thinking about it enough should allow you to know why you feel like this. Seeing a therapist / counsellor can help with that as well.
You might have a look here for a few thoughts that might help: emptyclosets.com/forum/coming-out-advice/175750-my-mom-doesnt-know-im-actually-her-daughter.html#2 There is a brochure where they state it has biological connections. People are individuals, and its a spectrum. So you might take the time you need to find where you feel comfortable. You might go through cycles. Where you feel more need or less need. It might also have to do with how much is repressed. You might think about looking for a good gender therapist. Not a gatekeeper but someone who might help you along . One question might be would you need a more female body to be a bit more happy. Another might be how you would like to be perceived. As said, i'd say take the time you need but keep at it. many *hugs*
