Why can I only read well in very bright light?

Hi, I've had eye problems ever since I was born. I was diagnosed with amblyopia (lazy-eye) when I was a child. With vision therapy, my eye became normal by the time I entered 1st or 2nd grade. I also have an astigmatism in both eyes. I've had prescription glasses lenses since.

This fall I enrolled into my first semester of college. I got contacts for the first time ever after visiting the eye doctor last summer. I wore them about every other day. I studied hard, got good grades, but near the end of the semester, I found that I had began to struggle when reading. I read well in bright light, though. For example: when I read on my kindle with its backlight all the way up, my computer screen at full brightness, or my iPhone with full brightness I can read clearly. I discovered that I can see the words on paper more clearly when I read in direct sunlight or with a flashlight and all the lights on in a room without sun. However, if there's no sun and no flashlight, I struggle.

The best simile I can come up with to describe my eyesight is that it is like grease on a phone. With more brightness, the grease isn't as noticeable, but when the brightness is lowered the grease is prevalent.

Do I need a new prescription? Is declining eyesight normal for an 18 year old?

You might i'm sure need a new or a stronger prescription but not for the contacts but for glasses.
in reading at night or in a room, at home, use a extra bright light ( from the hardware store) in a lamp which has the lampshade that is pointing downward over the book

I think you should see an ophthalmologist (an actual eye doctor, not an optometrist - that's what they have at eyeglass store)

Although you are young, maybe you have cataracts or some kind of reversible condition.