Trying To Conceive, Getting Unusual Short Periods, Having Pregnancy Symptoms, Reports Negative. Reason For Short Periods?

My periods are always regular, have been for years. My cycle is between 26 and 28 days long, and I usually have heavy bleeding for at least two days, followed by a couple days of medium flow before it stops. In June my husband and I started trying to get pregnant. I had a period on June 1st. Around June 20th I began experiencing pregnancy symptoms: burping, nausea, headaches, backaches, cramping. My period came on June 28th, but it was lighter than usual (medium-ish flow) and only lasted two days. My other symptoms eased up briefly, but returned a few days later, along with some new ones: frequent urination, painful breasts, and blue veins in my breasts. I took eight home pregnancy tests and they all came back negative. I then went to a doctor who checked for infection (negative), did a blood test for pregnancy (negative), and ordered an ultrasound (which indicated that everything was normal). I asked if there was anything I should do next, and the doctor said no. But I just got my period on the 24th and it s already over. It followed the same unusually short pattern it did last month. Should I be concerned, or is my cycle just changing for some reason? I haven t been stressed (aside from wondering what s going on with my body) and I haven t changed my diet. I m 28 years old and in good health