Specific Help: Paint tool layering lines

Hi,

I'm new to digital art. I've been drawing freehand for the longest time but I need to move with the times and I'm struggling so much. For starters, I got a new laptop that folds so I can draw, got Photoshop, and I've been practicing. My laptop came with a stylus, which was nice, but my experience so far drawing digitally keeps getting more challenging. 

Whenever I'm on a layer and I draw a line with the paint tool, it is always a lighter version of the color I picked, almost like its a lighter opacity, but, if you draw over it again, any place where the old line meets the new line darkens the cross-section. It is super annoying for coloring and outlining cause I can't draw in one stroke so I have to touch up, but whenever I touch a line I darken it and it stands out from the other lines; it's the same when coloring. I don't know if there is a setting I have to change/ if it's my pen/ or something. This problem forces me to either draw perfectly in one stroke and never intersect with the previous line, OR make a new layer for every line.

It happens when I draw in a new layer too. If I draw a line in a layer then draw over it in a new layer it'll still cross. However, if I were to erase the cross-section it'll get rid of it, but I'd rather not make a new layer EVERY TIME I want to draw over the previous work. Also, I'd like the full color I pick, not just a lighter version of it. 

If anyone else has advice, or even any words of encouragement that'd be also great! I'm losing faith in this and I really want to be a commissions artist and maybe start animating one day, but I'm struggling. 

Thank you for reading this and helping,

Brady