I havent worked out consistently in 3 years, and have been trying to get back into it cuz i miss being skinny and fit. Im around 175lbs at 5'5" which is...not healthy at all if you look at the amount of fat compared to muscle. So i decided to get off the couch and work out again, starting with simple, easy-breezy exercises like squats without weights, mind you 55 squats was nothing to me back then with 40lbs added. 55 squats later (nonstop 55) my legs give out and i collapse on the floor like a sad fat kid. My quads would not cooperate for the like of me. The situation here was pretty much "help me, ive fallen and i cant get up". Now that i cant even do simple exercises.. what can i do to get back up there?
Fitness is a sport of patience.
What you need to do is not trying to rush into getting fit again. You need to set goals 6 or 12 months from now and progress towards them.
Start with sets of 3 or 4 sets of 15 bodyweight squats. Bodyweight exercises are a great way to get back in shape before working out with added weights, do squats, push-ups, sit-ups, leg raises, pull-ups (or inverted rows if pull-ups are too hard).
You also need to make sure you eat enough healthy foods with the right nutrients and get ample resting time.
Simply enough, you've been three years out of the game, you're carrying more weight, and squats are more difficult than most people give credence.
The first thing you need to do is to rest long enough to be able to move without pain. You overdid it this time. You need to start with a lesser amount, and gauge results from there. There are any number of "X reps of this exercise in six weeks" programs available online. Here is one for squats. It's nothing terribly scientific, but it produces a guide for how many squats to do in each set. I got up to 30-40 in each set, 4 sets a night, when I last did it, before I got bored and moved on to something else.
The other thing that you may want to watch out for is overriding your body's natural signals via willpower. Some people are better at powering through discomfort and pain than others. I'm one of those myself. It's an issue because it means I'm prone to winding up unable to continue a program a few days later. If you find that you're prone to that sort of thing, intentionally pick a lower goal and work from there. It will mean that the first week or two will probably seem like you're doing nothing, but what you're doing is conditioning your body to the movement, getting it prepped. By the time it gets difficult, you will be significantly less likely to actually hurt yourself to the point where you can't get up in the morning.