Hi
I'm not an expert in psychopharmacology interactions. Your citalopram dose (20mg) + omeprazole shouldn't be much of an issue... However higher than 20mg/day citalopram + omeprazole is not recommended in the Citalopram Prescription Information

Talk to your doctor to switch from omeprazole to pantoprazole. Citalopram + pantoprazole is safter than omeprazole + citalopram according to this study: PMC4297217 (google PMC4297217 to read the study)

If you have a history of heart issues then you might talk to your doctor about switching to another SSRI. If Citalopram is working well for you there is no need to change it in my opinion and your doctor might consider an alternative to deal with your stomach issues.
Bear in mind I'm not a doctor or pharmacist but the best advice I can give to you is don't stop taking medication and make an appointment as soon as you can.