Morning erection problem. Else?

I am a 28 year old guy.  I have been masturbating since I was 20 years old.  4 or 5 times a week.  For the past 5 days I have not had morning erections.  Not just in the morning, but in the afternoon and night.  Earlier I used to get erections right in the morning, noon and night.  I'm not fat.  But if I masturbate or have sex with my lover I get an erection.  I have onemore doubt.  Actually I had sex with my girl friend a week ago. We had sex at her house.  She gave an oil to avoid dryness.  which is used by her brother. that oil name is "enlarge oil for men bigger harder stronger & longer". I used one or two drops on the top of my penis.  At that time I felt hot and burning for sometimes.  After 10 minutes I washed my penis and after that it was normal.  Is the oil causing my erectile problems or something else?