/u/RiotToyb is right, we don't do anything to force losing streaks.
There is a team balancer, however, which takes whichever 10 players ended up matching together and balances the skills of the players across both teams evenly, so both have the same chance of winning.
If you are matched with 9 players that are all a bit worse than you, the team balancer may give you slightly worse teammates altogether than the other team to balance that out. But it won't stack it against you, it'll just do a subtle balancing so both sides are even.
Ideally, all 10 of you are close enough in skill that this ends up not being very noticeable. But it's possible for the gap to be larger expected sometimes, and you do end up having to do more work than usual to carry the team.
We are working to make that only happen when absolutely necessary to get players into timely matches, so we have improvements across the board in the pipeline for that type of thing.
But outside that, streaks are normal even if matchmaking is 100% perfect. You can confirm this by flipping a coin and seeing how often you have streaks. Even perfectly fair matchups will still result in fairly long streaks now and then.