Thanks for your query.Based on the facts that you have posted it appears that you have problem of Premature ejaculation
and ave been taking SSRI inhibitors to delay ejaculation.
SSRI inhibitors are anti depressants and are known to have side effects like palpitation
and headache etc.
In absence of any major health issue cause of premature ejaculations is mind related and due to performance anxiety.
Following measure will help you to boost up your confidence and getting good erection.and delay ejaculation.
1) Practice regular exercise for 45 minutes followed by meditation
for 1/2 an hour in the morning.
2) Take high protein diet rich in vegetables and fruits and Vitamin A,C,D,E.and Zinc
3)Take anti oxidants like Almonds 5-6 everyday..
4) Avoid alcohol and smoking..
If you are married take your wife into confidence and discuss your problem with her as her co-operation is very important to resolve your issue.
Please consult qualified Urologist
to learn to modify sex techniques like start and stop technique or squeeze technique to delay ejaculation .This will take time to get the results which is definite to happen.