I don't know much about autism but I can say from my own experiences with doctors that a doctor telling you you are not diagnosed with something does not mean you aren't, it just means this specific doctor thinks you aren't. Doctors are too often trained to never trust you and dismiss whatever you might be saying.

I still think you should try and get an evaluation from a doctor if you think you might be autistic, because getting an actual diagnosis is helpful, but if the doctor says you're not, that shouldn't stop you from learning about autism, trying stuff out and seeing what sticks. No matter whether you actually are autistic or not, if living like you are autistic helps, then do that.