What Causes Irregularities In Periods?

okay so to start ive never been good with patience on things. So last month me and my husband had unprotected sex and he went inside me and I started what I thought at the time was my period 2 days later. Well I didn't think nothing of it anymore and then the last couple days I have felt to well and up to my normal self. I never said anything to anyone but then around 2 or 3 days ago my husband was staring at me and asked me if I was pregnant and course I laughed and said no. Well yesterday my symptoms seem to have got stronger ( not sure if that would be the right word ) and his mom ask him yesterday afternoon if I was pregnant too and he answered no. My symptoms include :: dizziness ( feels like I'm on a ride that is spinning me, even worse when I close my eyes ), nausea ( vomiting yesterday), feeling of being drained and weak, and a headache that seems to not go away, and frequent urination, and light cramps in my lower back and stomach. My period is irregular so charting and knowing the whole cycle thing I have completely just gave up with. With our first daughter I had no symptoms except tired and weak, and urination constantly it seemed. It has only been 4 weeks since but with irregular periods I skip months here and there and with our first I ended up bleeding as if i was having a period the first 2 months ( dr said it was because i was so irregular that it was all the blood that needed to be released to help make room). So is there a chance you think or could it be something else?