Hi I'm 18 Years Old And I've Been Experiencing Trouble

Hi I'm 18 years old and I've been experiencing trouble breathing, like something is crushing my chest and/or that I just am not getting enough oxygen even when I take deep breaths. I also have slight dizziness, both symptoms happen when I sit or stand. I also have had a headache all day and it's not due to dehydration because I've been drinking water all day and usually I'm fine by now. And for the past 2 months I've been constipated but today I was able to pass some stool but I still have lower abdominal pains but they aren't as bad as before I went to the bathroom earlier. I have no family history of any kind of diseases except for my aunt having a blood clot in her lung.