You started lifting weights to get stronger, increase your metabolism, and slim down. You focus on form and using the right amount of weight to prevent hurting yourself, but there's one thing you might be doing that could be really harmful.
Take a look at your feet. What are you wearing? If you're wearing running sneakers to lift, the extra cushion and heel support is great for absorbing shock when pounding your feet, but it's terrible for your alignment, and actually makes lifting harder. According to Dani Horan, a CrossFit coach and CrossFit Games competitor, the extra cushioning makes it harder to balance, and also puts your feet on an angled surface, causing you to lean forward. Whether you're using a barbell, dumbbells, or a kettlebell, this isn't great for exercises like power cleans, squats, as well as lunges, and deadlifts.
Just like you shouldn't wear cross training shoes to run, you shouldn't wear running shoes to lift. So get yourself a pair of flatter shoes like Nike Metcons or Reebok Crossfit Nanos. They'll feel a little weird at first, but once you get used to them, they'll help prevent injury and allow your legs full range of motion to be more explosive and efficient.