5 days late but spotting

Hiya everyone. Me and my partner have been TTC since I had my contraceptive implant removed in September 2015. I had it for the full three years so I'm aware it takes a while for your body to get back to normal. However exactly a month after having it removed I started having periods again and I come on on the 14th of every month like clockwork. However this month I'm 5 days late. I had light spotting on the14th but nothing since. I took a pregnancy test (pound one) on Tuesday and one today and they both show I'm not.pregnant. Any advice?