Yes and it was negative a couple of days ago. I have a blood test on this coming Wednesday
I'm a board certified Ob/Gyn and should be able to help.
There are a couple of things going on right now.
1) you may very well be in early pregnancy...however, if you are 18 days late for your period and the pregnancy test was negative...it is very unlikely you are pregnant. Pregnancy tests taken 7 days after a missed period are around 97% accurate and become even more accurate as time goes on.
2) If you are not pregnant...your symptoms are most likely due to a hormonal imbalance. This is usually cased when a woman doesn't ovulate, which produces elevated levels of estrogen for longer periods of time. This can result in mood swings, breast tenderness, etc.
Confirm you are not pregnant with the blood test you are planning on having done.
I'll assume it will be negative, but good to confirm that.
Then ask your doctor to give you provera for 10 days...that will produce a period in 1-7 days AFTER you stop taking it...this is sort of 'resetting' you cycle.
I'm here to help you.
Please give me an idea of what I can tell you that will make things more clear.