Hello Noobelele
A simple check - if your fingernail changes to white, you're pressing down way too hard.
Technique-wise, (a) make sure that your finger is perpendicular to the fretboard. Seen from the bridge, it's actually slightly less than 90 degrees, more like 80 degrees but not 45 degrees.
(b) your finger should be near the fretwire, not in the middle of two fretwires.
ON the other hand, check the set-up too. If you fret a note (any) and strum very lightly, do you hear buzz? Usually you don't. If you do, the action is waaaay too low and you need to get it adjusted. If you don't hear buzz but as you strum harder, you start hearing buzz? To some extend, it's normal. I personally prefer to get a little buzz as I strum hardest (I only pick with my fingers), and that's my *personal* setting. If you hear buzz as yu normally strum, then your action is too low. If you hear it when you fret, the likely culpit is the saddle being too low.
Where do you live (it would be a good idea to indicate in your profile) - someone can refer you to a decent store/luthier to look at your ukulele. A carefully set-up ukulele is fun to play and you will get better sound without unnecessary fatigue.
Happy Pickin
Chief