Three rules. That's the whole game.
1. Eat. Then eat more. Take your bodyweight in lbs × 18 - that's your daily calories. 1g of protein per lb of bodyweight, minimum. If you're not gaining 1-2 lbs/month, you're under-eating. Period.
2. Run a real program for 6 months. Stop switching every 3 weeks. Pick one, StrongLifts 5x5, GZCLP, or 531 BBB, and run it as written. Add weight to the bar every single session you can.
3. Sleep 8 hours and stop "doing cardio for abs." You don't have abs because there's nothing on the frame yet. Build the frame first; you can cut later.
What "build muscle" actually looks like for the first year: - Squat, bench, deadlift, overhead press, row, pull-up - 3-4 days/week, 45-60 min per session - Add 5 lbs to lower-body lifts, 2.5 lbs to upper-body lifts, every session you can - 4,000+ calories a day. Yes, really. Eat oats, peanut butter, ground beef, eggs, milk, rice.
If you're "skinny" after 6 months of this, you didn't actually do this. There is no third option.