3 missed periods

I am always very irregular for my periods but sometimes you can't help but think what if you're actually pregnant. Now that I am sexually active, it's sometimes scary having irregular periods because u always have that thought in the back of your mind like "what if I am pregnant?!"

I always use protection.

I haven't had any pregnancy symptoms like morning sickness or anything.

Typically if this is my 3rd missed period (my last period was July), how many months pregnant would I be ? Would I already be feeling symptoms if I was ? Should there be any weight gain yet?

Haha I am just asking this more as like a reassurance thing , but I am curious to hear the answers from maybe others who are irregular and go through a similar scare.