Judging by your match history last season, you were probably gaining small amounts of LP for wins and losing more for losses. Therefore, you had a pretty low MMR in Bronze V. Let's assume that you had a 400 MMR at the time of the reset (could have been higher or lower). A soft-reset hits ([1200+400]/2=800. Your MMR is now 800 before your provisional games.
For reference, 1200 MMR is widely accepted to be the difference between Bronze I and Silver V (but we don't really know this).
Now, you lost your third ranked game after the reset. The more you win early, the better off you are. Think of it as test/assignment grades in school. The more good grades you get early, the easier it is to have a high final grade. If you get lower grades early, you're climbing an uphill battle.
When it was all said and done, you won 7 games (good job!). This was calculated into your MMR which was 800 (probably 600 or so after your first game--maybe worse...we don't really know). You were placed into a tier based on your MMR. It seems as though most people are placed into the division just below where there MMR would put them. This could be because after the reset, the average MMR in each tier are defaulted back to normal, which is probably higher MMRs per tier than at the end of the season.
If your MMR is higher than your division (which many times it is after placements) when you win, you'll gain a lot of LP, and when you lose, you'll lose less. This is because the system is trying to find the correct division in which to place you. If your MMR is much higher than your division, you could potentially skip a division all together. This is rare, but it has happened to me once (placed in Silver V and skipped Silver IV).
Don't get discouraged and keep playing. Also, remember the new ranked promotion helper is live, so if you lose a promo series, then next time you're there, you get a free win.
