Brief Answer:
I suggest a possibility of a folliculitis Or a heat rash

Detailed Answer:
Hello. Thank you for writing to us at healthcaremagic

I have gone through your query and I have also reviewed the Image.

I can see reddish bumps on your lower back, most of which are follicular in location.
I suggest a possibility of either folliculitis Or a heat rash

-I would like to know if there are any symptoms?itching?pain?
-Do you have it elsewhere?
-How long since you have it?

As such it does not directly point to an STD if it is just localized to lower back.

-Do you have a history of an STD Or any history of genital ulceration?

Regards

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Brief Answer:
May apply a soothing lotion

Detailed Answer:
Hi.

It is likely a heat rash. I suggest you to apply a soothing lotion e.g calamine lotion, twice daily.

Regards

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Brief Answer:
Various possibilities for a rash on torso and arms

Detailed Answer:
Hi.

Other possibilities for asymptomatic, red maculopapular rash on torso such as this are pityriasis rosea, viral exanthem, drug rash.
However, pityriasis rosea usually evolves to form scaly patches which are oriented in a christmas tree pattern on torso.
Viral fever can present with a exanthematous eruption such as this and so can a drug reaction.
Treatment for most of these is symptomatic i.e soothing lotion and an oral antihistamine e.g cetrizine, only if itchy.
Syphilis is a great mimicker. The only STD which can present with a skin rash on torso or arms is syphilis.
However, since there is no history of preceding genital ulceration.
Moreover you also tested negative for all STD 6 months ago, therefore syphilis is unlikely, provided you had'nt had any risky sexual encounter during the last 6 months after you took tests.

Regards

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