Sounds like you’re in the plateau phase which is totally normal (and frustrating). The gains seem to come sporadically over time, and while I think there are some general trends they see, it depends on the golfer. The lowest cost swing speed radar is the sports sensor
one, it’s on Amazon for around $120-$130
Also I wouldn’t use one session as a measuring stick of your success (or failure). The only way to really know if you’re seeing gains is by using a radar. There are certain days/times where you won’t swing as fast, but when you track over time you’ll see trends.