Hey, I'm a 24 year old female also and I used for a very long time. I always had the same problems, I had such difficulty finding veins. I hate giving advice to help users keep using because I know what bliss and happiness i've found in my sobriety but I know how horrible it is to have dope and a set and everything right and just not be able to get it in you.
You are wasting your money and your time with IM and skin popping, though. You might as well smoke it at that point. Keep yourself really hydrated, when you're dehydrated it's almost impossible to catch the veins. I used to catch one in my right breast when I was really desperate, it's easy to find but hard to catch because it generally rolls so easy. Sometimes a super sharp, brand new set isn't the best. Dull it out a little bit, and you won't just stab right through so often. The veins in your legs are big, but deep, I've caught a few in my calf that worked out. Also try it in the bathroom, sitting on the toilet, letting your arm hang. The combination of the lighting and the gravity pulling the bloodflow seemed to help sometimes. If you can, get someone else to try. When worse came to worse I would go to the doctor's or the hospital and make up some excuse to get my blood taken. They would usually have to stick me a thousand times and get someone from the lab but they HAVE to get the blood so they figure out a way, then you can just do whatever they did when you get home.
But, please, look at yourself in the mirror next time you're hysterical because you can't hit a vein. Is this really the life you wanted for yourself? It's not the way it has to be. You have an advantage over other people in the fact that you just plain can't do it right anymore. You're totally wasting your money and your time shooting up IM or skin popping. You'll never ever catch a buzz off of it. You'd probably catch a much better buzz off of 32MG (8/2 x 4) of suboxone, honestly. that was the best part about getting off the dope and onto the suboxone: at the end I was just like you and couldn't hit a vein so I could get high off the suboxone and not the dope. Just a thought. If I can do it, anyone can do it. Hit me up with an email anytime, even if you just need someone to talk to who knows exactly where you're coming from, because I was there not too long ago. Someday you're going to get sick of living your life this way and you'll want help. Or you'll die. Nothing is going to change for you until then, and the happiest you ever are on a day to day basis is the happiest you'll ever be. If that's good enough for you, then more power to you, waste your young life away on dope. Just know that I go out, I party, I smoke weed, I fucking love my life. You don't have to become a nun or go to NA meetings (not that they hurt), or do anything people say you HAVE to do to get clean. You just have to want to get clean more than anything else. (which is so much easier said than done, I know.) There's more to life than sitting around getting high all the time and being okay with being bored. Anyway, I'm not judging you, just letting you know how i've come to see things coming out the other end of addiction.
I hope you find anything on this page even somewhat helpful.
Remember: Pain is unavoidable, suffering is optional. Be safe.