Yeah I only just started lifting and I've had back problems before so I'm taking it slowly. I only increase the weight when I'm really sure I can handle it.
Well, if you just started lifting, then use this chart
One-Rep Max Chart (Best 1RM Percentage Chart) - BuiltLean
Now that you kind of know your one-rep max for squat and deadlift, use that to gauge how much you can lift for 5 to 12 reps. Do your workouts based on lifting x pounds for 8 to 12 reps on medium to medium heavy days, and x pounds for 2 to 7 reps on heavy days.
Example, your one-rep max on squat is 176. There's no one-rep max on the chart, but you can see that 175 lbs in the first column equates to lifting 125 lbs for 12 reps. in your next medium weight leg workout, you may want to attempt 125 lbs for 12 reps, 130 lbs for 10 reps, 135 lbs for 9 reps, etc.
Then on the following week, you may want to have a heavy weight leg day. after warming up, you may want to work your way up to attempting 145 lbs for 6 reps, 150 lbs for 5 reps. 155 lbs for 4 reps, etc..