Perhaps you're worried your passed chlamydia onto the new girlfriend and are worried about picking it up again.
Have you told the girlfriend about this STD? Has she been tested for it since it appears you were infected at the time you first had intercourse with her and your posting does not indicate this was a protected act (perhaps it was).
Or, since your first sexual encounter ever resulted in a broken condom you may fear this happening again (it's unusual but not unheard of) and this is in the back of your mind during sex.
By the way, lasting "only" 20 minutes is NOT a problem; in fact, for many females this may be too long a time to have intercourse without causing pain and discomfort to them.
If you are in menopause, you are not going to produce much lubrication naturally. That's just the way it is. There is nothing wrong with using one of the many sexual lubricants available on the market today. Try experimenting with a few of these.
DHEA is POSSIBLY SAFE for most people when used for just a few months. It can cause some side effects including acne, hair loss, stomach upset, and high blood pressure. Some women can have changes in menstrual cycle, facial hair growth, and a deeper voice after taking DHEA.
DHEA is POSSIBLY UNSAFE when used in larger amounts and long-term. Do not use DHEA in doses higher than 50-100 mg a day or for a long period of time. Using higher doses or long-term use of DHEA can increase the chance of side effects.
Special Precautions & Warnings:Pregnancy and breast-feeding: DHEA is POSSIBLY UNSAFE when taken by mouth during pregnancy or breast-feeding. It can cause higher than normal levels of a male hormone called androgen. This might be harmful to the baby. Don't use DHEA if you are pregnant or breast-feeding.
Hormone-sensitive conditions such as breast cancer, uterine cancer, ovarian cancer, endometriosis, or uterine fibroids: DHEA is a hormone that can affect how estrogen works in the body. If you have any condition that might be made worse by exposure to estrogen, don't use DHEA.
Liver problems: DHEA might make liver problems worse. Don't use DHEA if you have liver problems.
Diabetes: DHEA can affect how insulin works in the body. If you have diabetes, monitor your blood sugar carefully if you are taking DHEA.
Depression and mood disorders: There is some concern that patients with a history of depression and bipolar disorder might have some mental side effects if they use DHEA. DHEA can cause mania (excitability and impulsiveness), irritability, and sexual inappropriateness in people with mood disorders. If you have a mood disorder, be sure to discuss DHEA with your healthcare provider before you start taking it. Also, pay attention to any changes in how you feel.
Polycystic ovary syndrome (PCOS): Taking DHEA might make this condition worse. Don't use DHEA if you have PCOS.
Cholesterol problems: DHEA might lower "good cholesterol" (high lipoprotein cholesterol, HDL). If your HDL level is already too low, discuss DHEA with your healthcare provider before you start taking it.
Why are you concerned? Are we talking seconds here?
Look; 20-30 minutes of sex without you ejaculating might sound just fine to you but frankly, to many women it is waaaay too long for the entire business. By then any sexual liquids a woman has produced has long dried up and what was once pleasurable is just plain painful. Many a female just wishes the darn thing would be over and one with 20-30 minutes into the event.
At any rate, perhaps you were just so happy to be back with the girlfriend your emotions just took over. Stop worrying about this; the more "extremely concerned" you get over this, the more you focus on the performance issue and, frankly, the worse the issue tends to become.
You don't have any STD. Neither does your partner. How would you then explain that each can give the other ANY STD if you both are STD free?
The obvious answer is that STD's just don't occur out of thin air because people engage in unprotected sexual encounters (oral or otherwise). One has to have an STD for there to be a risk to transmit it to others during unprotected sexual contact.
So the answer to your question "can you get STD's if both you and your partner don't have it" is "NO".