Eyesight getting worse

Hello!
So here's the story. My eyesight had never been too bad. When I was 15 I was perscribed glasses -0.25 for my left eye and 0 for my right. I didn't really wear them at all through high school to be honest because I really didn't need to. Well, when I went to university last year I noticed my eyesight slowly began to get worse. In march I went to see a doctor and I was perscribed -0.5 and -0.25. And that was still okay because I only needed to wear glasses in lectures and stuff, could see quite fine otherwise.
Well...Summer passed and when classes started in August I couldn't see all that well with my 6 month old glasses anymore. So in September I went to see the doctor again, got perscribed -0.75 and -0.5. And then I made the horrible mistake of trying out contact lenses. I don't know if it was just a coincidence but everything just started to go downhill from there.
I don't think I ever got used to them, it was difficult for me to focus with them even when I'd been wearing them for 2 weeks or so. I didn't even wear them every day, more like every other day. But anyway, every time after I'd been wearing them, I felt as though my eyes felt weird. My left eye felt A LOT blurrier than my right. And that even when I was reading books and stuff. It was like I could now feel the difference in the strength of my eyes, if that makes sense. It had never been a problem (there had been a 0.25 difference for years and I didn’t notice it). And it hasn't gone away since then. About a month ago I went to see the doctor again. Got a new perscription...again...-1 and -0.75. I also wear glasses most of the time now.
I understand that -1 and -0.75 doesn't seem like much, but as this time last year, or even 6 months ago, I wasn't really wearing glasses at all, then it's quite a sudden change. I'm just a bit worried. So I guess my questions are...Is it normal for eyesight to change so suddenly? Could it get worse? Can contact lenses affect the quality of vision this much? Can wearing glasses actually make the eyesight worse (I’ve heard this but I’m not sure whether to believe it or not)?
Sorry about the looooong story, but it’s just something that’s been bothering me. I hope someone can shed some light on what exactly is happening :)

[Ray T Oyakawa, MD]

These are insignificant changes and are probably due to changes at your age and increase reading for school.

Contact lenses properly fitted should not affect the quality of vision.  Soft lenses will not give as sharp vision as glasses or hard contact lenses for your range of refraction.

Glasses are set for distance.  Using distance glasses for near can increase your myopia.  You do not need glasses for reading.

Dr. O.

[fb109]

Okay, thanks :) But...If using glasses for near can increase myopia, howcome contact lenses don't? (Or do they?)
And is there any way to get rid of the uncomfortable feeling in my eye whenever not wearing glasses? I never used to feel the difference but now it's like I'm seeing double. Or is that normal?
Also, what exactly is astigmatism about?