from the history as narrated it seems the onset is rather sudden
regarding
testosterone level it is better to consult an
endocrinologist to find out the reason pf low level
you have not mentioned about your blood sugar level
it is very important .fasting and 2hr pp blood sugar level should be done
you should not be over weight
regular physical exercise will help
the worry about sexual performance before the act is hindrance to proper erection.
should have active support from partner in this situation
should pass tension free pleasant time with partner
.you have mentioned you get erection and it sustains
ITS GOOD THING
it seems you have some major degree of tension and you should be free of it.
regarding having issues is altogether another line of investigations and management
DO NOT WORRY
YOU WILL BE ALRIGHT