Welcome and nice to see you here
Of course my opinions are just that, I'm not a nutritionist. Having said that, I'd say that you likely lost weight well because you took in less calories. You might have lost a lot of muscle weight on that liquid diet (depending too on many other factors). I remember way back, Oprah winfrey went on a liquid diet too and lost all of her weight (thinner than she is now, in fact) and she said as soon as she started 'eating food' again, it came back with a vengeance. I think she said she'd gained 5 pounds by the end of the week.
I have never been a believer in slim fast products. They prey on people who need/want to get weight off quickly (like there is anyone who doesn't want it off quickly). Mostly what is in that stuff is chemicals and junk, and you mix it with milk (probably the only healthy part about it). Again, sorry slim fast, this is just MY opinion.
Anyway, perhaps you might consider picking up some reading materials on foods and nutrition, or make an appointment to see a regular nutritionist who could evaluate your situation better.
Having had success with slim fast I think, you may not be giving your new plan enough time to work. Your metabolism may need a few weeks to try to adjust to the new eating pattern? I'm really not sure what kind of long term effect a liquid diet may have on your metabolism overall. Read some books, and keep doing what you are doing!! Doing some physical exercise and weight training is definitely a positive step for sure, don't get frustrated!!
This is a learning process for all of us, in a world that continually attempts to prey on the overweight crowd with their constant gimmicks and quick fixes.
You CAN do it, you just have to learn what will work for you long term, that you can live with. Good luck and hugs to you