...A FEW months ago I was circumcised because I was having a few problems.

Ever since then, my sex life has been suffering, and I can’t maintain an erection for more than a few minutes.
...
Before my operation, we had a great sex life and I’d never experienced any struggles.

It’s not uncommon to experience erection problems after a circumcision but if your problems are persistent there may be more to it.

Sometimes circumcision scars have been shown to contain damaged nerve fibres which do not allow for normal sensations.