I've read both of your points and I will take it upon myself to act as a third party if you will.
I'm agnostic and the definition for agnosticism is the following:
The view that knowledge of whether or not God exists is unattainable, that we cannot be justified in believing either that God does exist or that he does not.
Now as MC has went over:
If everything that exists must be created/had a cause, then that means God himself must have been created/have a cause.
A common example used my theists (not saying you are using it exactly, but it helps get my point across) is the watchmaker analogy.
"If you find a watch on the road and pick it up, you instantly realize that this watch must have been created. Complex things cannot exist without a creator to design it".
This is very, very easy to debunk. If complex things require a creator/cause, and if God is far more complex than a watch or humans or anything we know of, then that means God must have been created by an even more complex being, and that that being must have been created by an even greater complex being, and so on and so forth.
I absolutely agree with this as a stance against the belief of a God and I'll add that many theists (not necessarily you OP) have often been content to say that we are unable to comprehend God, that his being transcends our day to day experiences and that our concepts, which are derived from such experiences, cannot be used to describe him. If true, then this might be thought to count in favour of agnosticism; if we cannot comprehend God, then how can we reason with any confidence concerning his existence?
Of course on the other hand there is the argument of uncertainty. There is plenty of incorporation of mathematics and science into the backing of beliefs but the truth is, we are constantly finding out that equations thought originally to be true are now being disproved. Point is, our mind is constantly developing and to completely rule out the existence of a God through logic is very fallible considering logic is never set in stone.