21 year old female experiencing shortness of breath

Hey guys. I’m a 21 year old student. I’ve been experiencing shortness of breathe all day for about 3.5 weeks now. I also feel like my throat is thickly and as a result I have to cough every now and then. I also feel like I have excess mucus in my throat as I’m constantly clearing my throat. I’ve been to the ER 4 times now, every single time the doctor tells me I’m fine & that Nothing is medically wrong with me. I’ve never been anxious person & I don’t feel like this is health anxiety. I feel like something inside me isn’t right. I just don’t know what to do? Has anyone experienced this? What helped you? Thanks so much guys.