Pregnancy test negative, but had pregnancy symptoms and my period was early

Hi,i am 25 years old female,my period is 28 days cycle,last month i.e july,i have it 3 days early with very light blood and clear mucous which last for one and half day. Later I have lower backache,veins in my hips,legs,palms,in my breast also with nausea,and bloating.... then in August my period is two days early then it's normal... I even tested for pregnancy but it came back negative please tell me what's my problem