Hello, I've Been Taking Clindamycin For 3 Days And Suddenly

Hello, I've been taking clindamycin for 3 days and suddenly today a strong stomach ache appeared. almost 4 years ago I had a Nissen fundoplication and since many years ago I've had stocmach problems (ulcers, gastritis, etc). Sincé the procedure I've improved a lot.
I'm cancelling the clindamycin as we speak, it was prescribed due to a throat infection (with cough). I just took one omeprazol. Shall I take another antibiotic to complete the treatment?
thanks
Luis P. MAle, 45, 163 ponds, 5'6.