Weird vaginal bleeding every 3-4 weeks, could I be pregnant or just irregular period?

I've been getting vaginal bleeding like periods that are irregular, like some last 3 days and one day will be heavy and then it just fades away by the third day. I had sex with a guy in late June. My senses have become 20x stronger in the past little while and I'm an emotional wreck half of the time. Not to mention my cravings. I also feel like I look different in size. I've been chunky and I lost all my weight but I see my stomach forming in a different way and it kinda scares me. Is it possible to bleed every 3-4 weeks when you're pregnant? Have any of you experienced something like this during your pregnancies?