Will my retainer straighten my teeth again?

I should not have stopped wearing it, I was stupid. I haven't been wearing it for a year and a half now. The top teeth are still straight, but small gaps are beginning to open up. The bottom teeth are still straight with the exception of 1 or 2 teeth that are crooked which really aren't that bad. I have a regular retainer made out of plastic with the wire. The top one fits in easily, but it does not touch the front teeth, I'd say there is a .5-1.5 mm gap between the front of the retainer and the back of my front teeth. The bottom one is definitely more snug and more difficult to get in. It almost feels like it does not go all the way in although it appears to. It is a little painful after I wear them for a while, but it is mostly just annoying/uncomfortable. Based on the information given, will the retainer correct the gaps on the top row and the crooked teeth on the bottom? Will it prevent the problems from getting worse? Can I get away with only wearing it at night? Thanks!