Skin spots

I have these brownish spots in my hands and I''m not sure what could be causing them. They appeared very suddenly, I thought they were age spots but I doubt it. I''m only 23.

They basically appeared over night, someone told me it could be the lemon, since I made a lemonade and then went out to the sun and lemon it''s supposed to make the skin more sensitive to the sun. But I''m not sure sure as I got more after that day. I put sunscreen on my hands every day after I first saw them, and I still got some new ones it seems, I have this big one on my left hand, really strange and it''s not too round. They are totally flat, not a different texture, just darker.

I noticed that, from the first ones I got, one seemed like it was peeling, and I started to mess with it and it did seem like a bit of it came off and there''s fresher, lighter skin below it but I''m not 100% sure. The sun has been really tame lately because of the rain, so I''m doubting it''s sun, plus like I said, I''ve been using sunscreen everyday.

They don''t hurt at all, but I hope they aren''t permanent. Then I thought it could be my dog''s leach, he pee''d on it when it fell out of my hands and I had to grab it anyway so I don''t know maybe some kind of infection or urine being acidic reacted with the sun? and the leash is not 100% clean yet, even though I wash my hands as soon as I''m done walking him, I finally washed the leash today.

I''m just trying to narrow it down to something. I''ve also recently gone to this new park, where I play sports, walk my dog, maybe a plant is causing this?