won 7 matches in a row and get 14 lp per match

consistently have a positive winrate. If your lp gains are low that means you are matched with people lower ranked than you (your mmr is low for your division)

If you maintain about a 53% winrate your MMR will climb up to your division and then your lp gains will increase as well. if you maintain a 60% winrate it will jump even faster. They have it increase at a slower rate though to avoid momentum swings plummeting you too low or getting you too high. Essentially you have to prove the system wrong on where it thinks you belong consistently.

The reason is probably that your winrate is below 50% atm. Generally, the higher your win rate, the more LP's you gain.

youre at bronze 4 with a 49% winrate try to just keep the wins up and it will give you more gains

Division 5s are tricky. At Bronze 5 it is possible your MMR was as bad as what would be Bronze 9 if such a thing existed. Now that you climbed to Bronze 4 it shouldn't be as bad.