The beauty if science is that belief isn't required. I'm not a physicist, but if you're coming out and saying "I believe the big bang theory is BS" I expect at the absolute very least some kind of reasoning or evidence of why you hold that position, and pointing out the flaws in the well established body of research and evidence that supports the theory. Ideally you'd also show how your alternative theory holds up in the context of all the other things the big bang theory helps explain.

Having said that, from your question I gather you seem to think the big bang somehow explains what happened before the start of the universe. Which, AFAIK beyond suggesting it will be extremely challenging to figure that out, it doesn't (make claims about what came before the big bang).

I'm sure there are many here who are way more knowledgeable on this than I. I look forward to reading their replies.