Visual acuity problem?

What I want to know is, why do my glasses never entirely fix my vision to 20/20? I go to an optometrist or to an opthamologist every year to get an eye exam done, and the perscription keeps getting strengthened (as is appropriate, I guess, as I am only 18). I know that not all of the doctors can be giving me the wrong perscription--different doctors have given me similar perscriptions each year, though always my perscription is strengthened. Yet I can still see only about 20/40 or 20/50.

It's not like my eyes are so bad that nothing could be done to corrrect them--my last perscription from an opthamologist was: OD: +1.00 diopters farsightedness, +1.00 diopters for astigmatism with a 120 axis; OS: -3.25 diopters nearsightedness, +.50 diopters for astigmatism, with a 90 axis. It's not like that perscription is particularly severe, I think.

Is it possible that my eye doctors keep assuming that my eyes are getting worse and strengthen the perscription, while it is too strong?

In addition, I had lazy eye in my right eye as a child, and it was corrected. I don't see halos today, so I don't think I still have lazy eye, but I feel as though my vision is almost as blurry for seeing distances in that eye with or without the glasses.

Not everyone can get 20/20 even with best correction
(Sorry, somebody's got to be below average, that's how they put averages together!)
Nor does it mean your eyes are unhealthy, though with below average acuity that possibility should always be eliminated.
Your doctors will have been looking for that.

The difference between your two eyes is a strong clue, together with a history of lazy eye, that your vision may be normal *for you*.
This is not that rare, though 20/40-50 in the best eye is a little low.

One simple check to see if glasses may be off prescription is to hold a 1mm pinhole in a piece of thin card close to an eye, and look at a letter chart, or other distant detailed object (with glasses on).

If the vision is definitely better through the pinhole, this needs to be followed up. (though better glasses can't *always* be made. )
If the vision is no better, or worse, the glasses are as good as they can be.

If you were my patient, my suspicions to be eliminated would be:
Some form of amblyopia
Nystagmus
Keratoconus
low-grade congenital cataract
Hereditary macular problems.
I would be surprised if these have not been considered and ruled out.

But the vast probability is that there is nothing that requires active treatment beyond best glasses.

(Optometrist, retired.)

"Is it possible that my eye doctors keep assuming that my eyes are getting worse and strengthen the perscription (sic), while it is too strong?"

no. no one needs you to find out what your Rx is. they only need your responses to find out what you actually prefer looking through. its a common misconception that patients think they are "choosing" their own prescription. but in reality the doc already knows what your Rx is before they even start asking you questions. the "refraction" or asking questions part is really just for fine-tuning.