late period, negative tests

I'm 25 yrs. old and my husband (also 25) have been married for five years now. We've been trying to get pregnant the whole time. This time I thought it happened. My periods have never been late, since I was 14. Always early, NEVER LATE. My period was 4 days late this time. I was estatic. my husband is gone every other week, and wasn't home yet, and I wanted to tell him in person. So I ran out, got two pregnancy tests, took them- Negative. Okay, i thought. It's just too early, and they weren't exactly name brand either. No big deal. I'll just wait 'till hubby gets home, tell him the news and get another test. I get up this morning and go to the restroom, and I see pink. Crushed. Heartbroken. Failure, again. So, here I am sitting in the bathroom bawling. I mean the kind that makes it hard to breathe. Asking over and over "why?" "What have I done?" "What's wrong with me?" Everything in my gut was telling me "this is it. You're finally pregnant." After I took my first pregnancy test and it came back negative, I wasn't even phased by it. I knew it was wrong. I went to the kitchen, got a dove chocolate and when I opened it up, the message said "follow your instincts". I smiled, said a prayer for this to be really true, and went about my day. It was like that for four days. Sheer happiness. I didn't tell anyone because I wanted it to be a surprise. Now this! My husband comes home tomorrow, and I have to tell him that once again, it didn't happen. I just don't get it. Last months was lighter than usual, only went about 5-6 days, then This one is four days late. I didn't even feel it coming on. I had no period symptoms. No cramps, no breast tenderness( and mine get sore, bad), no lower back pain. None of it. I've read about implantation bleeding, but i don't know if that comes with small light cramps or not. If you read this and can help me, please do. I'm losing my mind here.