Has the sun become way brighter the last years? Up to last year, I never got blinded by the sun in everyday situations (e.g. running towards it), at no time of the year I was. But since last christmas, it occured to me more often that I cannot watch in the direction where the sun is because it is so bright that it really hurts me.
My mother and my roommate have observed the same phenomenon independently of me.

This, of course, is only anectodal evidence, which is practically worthless. We all get older and we may have the same kind of "photophobia", or we just forgot about being blinded the last few years and just now consciously felt an remembered it.

Therefore I want to ask this question: is there any objectively observable increase of brightness over the last few months and if so, why?
The Sun's luminosity is stable to 0.1% - it varies slightly in response to, or associated with, levels of solar magnetic activity (Solanki &amp; Unruh 2012).

This variation would not be perceptible and is completely outweighed by the $\pm 3.4$% variation caused by the non-circular orbit of the Earth (the Sun is closest in January). 

Obviously, if you live in the northern hemisphere, then the Sun is generally higher in the sky now (in May) than it was in December. Its direct light is less absorbed/scattered by the atmosphere. This is a much more perceptible effect. It could change the visual brightness by tens of per cent, and by even more in the short wavelength blue part of the spectrum. That is the only physics-based explanation I can offer.