i have to say i rather like your art! the colours are nice and soft and your grasp on anatomy is pretty good! i do agree that some of your poses look a little stiff.
what i would recommend to alleviate that, is to look into line of action and try doing quick gestures of more action-y poses. you can alleviate this by thinking about your character's center of balance, and how you can move it to make your characters' poses look more natural.
for example, in the last link, with the blonde girl in overalls, you have her sitting straight up, making her look like shes rather shocked! if you wanted to do a similar pose with a more relaxed pose, you might want her to slouch a little, or rest herself on her knees or something similar. along with that, in relation to anatomy, i'd pay more attention to the length of her legs and how her calves measure up to her thighs.
here is a similar pose from senshistock! (who i recommend if youre looking for stock photos to reference or practice gestures from)
notice how she looks a lot more relaxed, her back curled so her head is just forward from where her pelvis is rested.
definitely brush up on your poses! look at how people stand as resting, and how they don't always stand straight and with their balance on both feet. try drawing a pose where they rest their body on one foot and just support with the other. try even taking videos & pictures of yourself or your friends (with permission!) just sitting around or goofing off.
your 2nd link shows you're completely capable of creating interesting poses! that one doesn't look boring or stiff at all!
as for trying to find ways to invigorate your art, a fun exercise i find is to try drawing in other artists' styles! even try your hand at styles you don't normally draw in! study how they pose their characters, the way they construct the face, the way they use colour and shading.
as for your lineart, i'd look into practicing line weight! just draw lines over and over in different pressures and speeds. you can also try doing coloured lineart to change things up and add interest. i sometimes colour the lineart based on highlighted areas! i know in my program you can colour your lineart by right-clicking the lineart layer and select 'make quick clipping group'and just putting colours on a separate layer above your lineart but im not sure how that'd work on your program.
also please be careful with how you grip your pen! if you're gripping it too hard you can fatigue the muscles in your hands and make it painful to draw! make sure you're stretching your wrists before and after drawing!
now for colouring, one fun way i find to make your art 'pop' is to trying shading and highlighting with colours next to your base colour on the colour wheel! for example, if your base colour is a blue, you might want to shade with a dark purple, and highlight with a light green! heres two tutorials that kinda illustrate what i mean: (one) (two) (i personally love using colours further along the colour wheel to shade hehe)
i'd also recommend studying up on contrast for your colouring! consider how much contrast you want in each art piece and how it works together to create feeling! heres a good tutorial that talks about contrast! a good way to check the contrast in your art is to fill a new layer with grey and put it at the top of your layers and put the blending option to color so it'll make every greyscale without actually getting rid of all the colour.
also if you're feeling your shading looks messy, try looking into other shading styles! such as cell-shading
i really like your art! theyre very pleasing to look at and your characters are so cute! i hope these tips help you :) if want any clarification on anything i said, let me know! i know i said a lot so its no worries if you need me to explain certain parts better!