What do you think?

So first of all my period is pretty irregular, this app is usually pretty on the dot but it has occurred when it’s wrong or I have missed a period once in a blue moon. That being said I completely missed my period for April, about 2-3 weeks after I missed it I took a test and it came up negative. Finally I got my period this month. It started pretty heavy (which is normal) but it dwindled down pretty fast and I only bled for three days ( when I usually always bleed for 5). And now, two days later I’m feeling really sick: headache, having a hard time looking at my phone screen, fever, nausea. Is this just coincidence that my body is acting like this? Anyone else have any similar experiences?