How do I fix bad MMR?

For context, I've been in silver 2 for over a month and up until recently I had been gaining 20-25 lp per win and only losing a consistent 15 per loss with most of my games ranging from silver 1- gold 4. Recently, I duo'd with a friend in silver 4 and we lost a bunch of games. Now I'm in a weird spot where I still lose 15 per loss but I only gain 16-17lp per win. What could've possibly messed up my lp and how do I fix it? I've kept a consistent 54-55% win rate in silver 2 and I want to move up, but the past few wins have been discouraging. When I duo'd with my other friend in silver 3 he got the same weird lp changes too.