Question about Vipassana

After focusing on my breath during my meditationsessions a couple of years I desided to start practisiing Vipassana. I will like to add that I have never been on a Vipassana-retreat (yet). Im still very interested of practising it, but after some months of doing it I have some questions about my practise: I tend to struggle to be aware of my tougths as they ocour and when I become aware of that Im following a train of thougths later I "Choke" them or supress them(?). They will stop instantly. This will go on and on during my sessions and it leaves me confused if I am practising this in a productive way. I guess I still have alot to learn about this way of meditation, but Im still interested to see what you think about this and if you got some advise. Thanks!