Mourning her son, Sharon Dempsey worries that a nightly sedative may harm the baby she's expecting

We have told Kate, our daughter, about the new baby. She cried because she is so happy. Usually she cries because she misses Owen. She begins making plans about the baby, where it will sleep, what we will call it. Kate is 11 years old. I realise I will have a toddler and a teenager at the same time. Oh joy.

I don't feel comfortable telling people about the pregnancy. I could have tried to keep it secret until I had reached 12 weeks but my sickness was so unrelenting that I couldn't hide it. I look wretched and feel dreadful.

I wake every morning to a rising tide of nausea. I am fooled into thinking that if I eat something the sickness will ease, but more often than not I promptly bring it back up again. Aftershocks continue throughout the day. This shouldn't be a surprise - I had hyperemesis, an extreme form of all-day pregnancy sickness, with Kate and Owen. At nine weeks into Kate's pregnancy I was in hospital, dehydrated and on an IV drip.

I am not as severely sick with this pregnancy as with my previous two but I am not coping with it well. I want to be resilient and get on with it but all I can do is moan and feel sorry for myself. The sickness wells up and with my head hovering over the loo, all I can think of is Owen and how sick he was during the 16 months of chemotherapy. It wrecks me.

He was so emaciated and weak. The toxic warfare ravaged his little two-year-old body, leaving him in need of blood and platelet transfusions. I desperately wanted to feed him nutritious, healing food but on a good day all he could manage was a banana and bread and butter. I would carry him on my hip, like a little monkey clinging on. His legs were so wobbly that he couldn't walk far. Vincristine, one of his many drugs, caused joint and muscle pain, leaving him sore and sick. I was poisoning my son in the hope of curing his brain tumour.

There is nowhere as lonely as a hospital ward at 4am. Owen would awake, throwing up violently, retching until his stomach was devoid of all liquid. Then I would sit in a hospital chair with Owen snuggled up to me with his "nightie" - my old satin nightshirt, which he used as a comforter. He was attached to the drip stand and we would be lulled by the rhythm of the IV pump doing its job. We spent countless nights like this, watching the city come to life from our vantage point overlooking Belfast, both of us exhausted and depressed.

I have a private appointment with an obstetrician for an early scan. The NHS appointment will be in the 14th week of my pregnancy and I am too anxious to wait.

The main reason for my anxiety is that I have been taking the sedative diazepam at night. I am terrified that I am harming my unborn baby but I have been on the 2mg dose for so long that it has become a habit to help me relax enough to sleep. My GP has been sympathetic, knowing that I am torn between getting some sleep or spending yet another anxious night in Owen's room.

The consultant is not impressed. Although he doesn't believe I am harming the baby, he is not willing to condone the taking of medication. I try to explain the reason - I have nursed my child through cancer and watched him die in pain, I am traumatised and in the depths of grief. He tells me in that arrogant way that seems to be the reserve of some consultants that he is only interested in the welfare of this child.

I thank him for his time, hand over my £100 (€144) cheque and leave with a print-out and video of the ultrasound. Going private doesn't suit me. The pre-warmed gel squirted on my stomach was the only consolation.

Bring on the NHS.

• Second of a monthly column