do you have the addon REFlex ? it tracks your arena matches, and more importantly, the MMR of each match.
what kills your MMR is lose streaks the most, and losing to opponents with way lower MMR
if your MMR is not healthy (way below your CR), it is important to have a win streak, or else it will take a while for it to catch up because you can’t just sit at 50% winrate in this situation because losses remove you a lot of points, win don’t give you many and your CR will go down to stabilise around your MMR.
so as mentioned above by Aryash, the only way out really is a win streak to get your MMR above your CR. then you can play around >50% winrate for a while and it will climb.