Little lp per match

When I play ranked I gain 12 lp. Im aware that i have a 39% win rate but it says my mmr is normal for my rank even though I only gain 12 lp per match and lose 19. So basically ill be bronze for the rest of my live and ive been playing normal's and taking a break thinking that will do something and recently coming back after months and only gaining 12 lp.

Please tell me how i can gain more lp per match and back up to its normal 17-23. Thats how much i was gaining in my previous rank