Is this normal,or is my body unbalanced ?

My last period was april 28. I have a 28 cycle like clock work. Me and my husband have been ttc. So I was suppost to start may26. Now here's the weird part on the 17 of may I got these pains in my left said. So I went to the bathroom and has a light brown/red discharge. (Only one time). Then the 26 came and nothing. Finally the 29 I started spotting and having lil cramps on and off didn't last long. I having no pains at all cramps ect .... and my period is light. Now what I don't get is I have very very bad periods . I cramp bad threw out almost the whole period. Which is 6-7 days and very heavy. I also took a pregnancy test on may 28 but it came back invalid.