I have missed my last 4 periods which are always on time/regular. For the past 3 months I have had severe cramping pain in my lower abdomen, particularly on the left side. Of late the cramping has become extremely painful to the point of cripling over screaming, i've also had a lot of pressure on my rectum which is not due to me needing to use the toilet as well as lower back pain. Following a doctors visit she tested my hcg levels which came back "negative" and I was sent home with a referral to a gastroenterologist to see if he could provide further details.
Just one week later I was taken to the emergency department with excruciating cramps and lightheadedness/dizzy feeling. After a very brief description of my pain and other symptoms the dr proceeded to tell me I probably just have irritable bowel syndrome (with no symptoms) and sent me home to take buscopan.

I have a very negative feeling about both doctors advice as this pain has not gone away and is only becoming more excruciating. I have had no bleeding and an ultrasound found no gestational sac - but is it possible I have an ectopic pregnancy which is going undiagnosed?