Late period

My period was supposed to start on Monday 18th April 2016 and it still hasn't started and today is Saturday 23rd April 2016. I'm still getting cramps and my boobs hurt so much that I can't let my partner touch them. I've had no spotting. 
I'm too scared to do a test as I'm afraid of a negative result! 
I really want to be pregnant and myself and partner have been trying for 3 years. 
I am very slim which i no plays a massive part in conception but I really struggle with my weight. 
Ladies should I take a test or is it too early ??
Thanks you xx