Riot working against me in SoloQ

Last night I was plat 5 and ecstatic about getting my plat border on tuesday. I had lost 2 games and was sitting at 0 lp before I played a game this morning. Unfortunately I lost another game, but this time I was demoted to Gold. Since when can you be demoted from plat to gold by only losing 3 games? And it's not like I have been losing consistently, I won 3 games in a row the day before I got demoted. Now I'm gold 1 and I have one day to get back to plat before rewards are given out. Only problem is winning games gives me a static 10lp while losing games makes me drop 20-25lp. Also the teamates I am being qued up with are Gold 5-3 while the enemy team is in the high Gold 3-1 range. Does Riot not want me to get the plat border I have worked so hard to achieve? I grinded through gold for 3 weeks and made it to plat as fast as I could. Now with only 3 losses I'm back in gold the day before rewards are given out. This is just unfair. Now I have to grind all night to get back to plat which might not even happen. If you're gonna demote me at least make it so I have a chance at getting back. Just another example of a poor ranking system.