Trust your instincts.
See your gp, and stand your ground. Don’t be fobbed off - quite often a ‘wait and see’ holding pattern is initiated, but try to ensure you are in waiting lists for actual assessments, rather than waiting lists for eg parenting guidelines or similar.
Take a look at the M-CHAT test - it should be easily found by googling. If you can take that along and point out where there are areas for concern, you might be taken more seriously. It only takes 5 minutes to run through, and it is a screening tool for whether a child warrants further investigation.
I knew by 6 months old tha there was something seriously awry with dd1’s development. She was dx’d at 2.5 with severe ASD and learning difficulties. It took until she was 17months old for anyone to take me seriously as she was so young and they all took the ‘wait and see’ approach - it’s just lost time, tbh.
I knew with dd2 by the time she was 8 or 9 months old. Different kettle of fish entirely (no learning disabilities), but still not NT. She wasn’t dx’d until she was 7 (ASD) as she is so high functioning (and the testing system isn’t really great for catching girls, tbh).
Ds is the least affected by his ASD, and even with him it was crystal clear by the time he was 18 mo the old.