How early can you catch on that you're pregnant? What are are signs and symptoms to look out for? Whats the earliest sign to notice?

I didnt really have any signs. I felt like I was slightly bloated but didn't think much of it. At 3 weeks pregnant I had a can of alcohol and made it not even half way before having breathing problems and unsettled stomach. That was what made me go to doctors and they did test to confirm