Severe stomach pains and acid reflux with Clindamycin?

The better question is...

Why have you been taking antibiotics for so long? Antibiotics kill both the good AND bad bacteria in your digestive system. I am almost 100% sure that's why you have stomach pain and acid reflux...because you don't have any good bacteria. Stop taking the antibiotics and start taking a (good) probiotic supplement or eat yogurt high in probiotics. This will replenish the good bacteria.

It is not normal and you need to speak to your doctor right now. If you develop an ulcer that 'burns' into an artery you can lose a LOT of blood (happened to me.) A worse case scenario is that the ulcer perforates right though into the body cavity. If you start to pass black, tarry stool and/or if your pulse starts to race for no reason, have someone take you to the ER.

Antibiotics in ulcer-prone patients really must be taken with a full glass of water and even then they can be problematic. It's not so simple as just taking antacids or acid-suppressant drugs to stop it. Sometimes if you take them or if you take something like Gaviscon it can stop the antibiotics working properly. Hence the need to ask your doctor.

I really do not know why you are still taking antibiotics after a month. A week is the most in the UK. You are way past the time for infection, the sockets should be closing over.

Stop taking it.