Squats are supposed to be tiring especially if you don't do them often enough. Thats why they are so good for building overall strength you are engaging like 90% of your muscles in some way or another not just legs and core but even you arms and shoulders are somewhat involved in holding the bar not to mention a lot of stabilizing muscles that don't normally see a lot of work.
If you want them to be easier you need to do them more not less and make sure you get adequate nutrition and sleep after so you recover and build. Also keep in mind that if you are say 30kg overweight and are squatting 70kg thats like a skinny person squatting 100kg so really you are doing more than you might think.