What Causes Light And Short Periods Along With Severe Mood Swings?

hi for the last 2 of my periods it's not really been a period it's been more of a pinkish brown discharge that lasts for a day and has gone away and I'm just wondering what this could be? Ive also been getting a lot of symptoms like lower back ache, frequent headaches, hot flushes, mood swings, a bigger appetite, cramp at the bottom of my stomach and legs, little stick like pains in my side, tightening in my stomach, pressure in my stomach, I've been urinating a lot more frequently, feeling dizzy, feeling sick every morning and sore and tender breast and I've taken a few pregnancy test which have all been negative but the same thing happened when I was pregnant with my first child I never got a positive answer till I was 13 weeks pregnant and I'm just worried it could be the same think again?