What Causes Abdominal Bloating,back Ache,headaches And Larger Breasts?

Question: hi I am a twenty four year old with a four year old son myself and my partner have been trying to conceive for the last two months my last menstrual period was on the twenty first of april and my cycle is usually a five week cycle on the twenty first of may instead of having a period I had brown discharge for six days thought I had a UTI as I am prone to them therefore sent a sample to my GP it tested negative for infection doctor thought it could have been an implantation bleed however on my son HCG was not detected until seventh week of pregnancy have had abdominal bloating which is constant back ache, headaches and larger breasts GP have performed both urine and beta HCG which gave a negative result they refuse to give me an ultrasound as they have no evidence that this is needed however now six weeks without a period an enlarged abdomen and the general feeling of being unwell I have decided to pay privately for a ultrasound which will be preformed on Monday, although the possibility of being pregnant is rare are there other possible causes of these symptoms as they are quite worrying especially as my usual period lasts seven days and requires myself to wear at least to sanitary pads due to the intensity of the blood flow
thank you in advance