Am I pregnant?

For the past 3-4 months my periods have been very short and light compared to what they normally are. Only lasting 2-3 days compared to my normal 5-6 days. Also I only have to wear a panty liner because it's so light. I have also been gaining weight! I have never had to worry about my weight in the past. Has anyone experienced bleeding or spotting during pregnancy? Or been several months pregnant and not known?