You never had sex without a condom?
False positives are rare but they do happen. Expect your next result to be negative because it will be.
First I have a few questions, because if your story is true you are a very unlucky person to get a false positive and next to that an indeterminate WB. But then a new test would give you a negative result! (why haven't you called for the situation on the latest test?)
1) why did you test recently?
2) Did you really haven't had any unprotected sex of IV drug use after your negative test 3 years ago?
3) why did you do the test 3 years ago? and if you had a risk before that test was the test done outside of the window stage?
4) Why did you take the recent HIV test if your last test was 3 years ago and was negative?
These questions because:
1) unprotected vaginal sex eventhough it's a risk, it's not a high risk like anal sex. Also you mentioned you only have done one unprotected act, so that's also lowering the chance of being infected. (because not many hetero people are infected compared to MSM)
2) eventhough you haven't had any unprotected sex for 6 years and you did a hiv test 3 years ago which was negative.(everyone would have produced antibodies by then). If the new test would be positive and if they confirm you would be really positive (which I really doubt with the information from you I have) this would mean the risk have been after your test 3 years ago or the risk was too close before your test 3 years ago.(window period)
Indeterminate WB happens:
1) there is an interference in your blood, like other virusses which also produce proteins and with the testing makes a faint line on certain patterns so that they can't make out if the lines are truely because of the HIV protiens or not.
2) within window period, so the infection is very recent.
Elisa false positive happens also once in a while, because they are so sensitive for the P24 protiens and also for the antibodies.
Just to add I want to add a link from the expert forum:
As you can see the HIV professional Dr. Hunter is reasuring the questioner about having a postive ELISA result and indeterminate WB, but afterwards the result is Negative. and saying that if it's indeterminate WB in most cases the person is not infected.
If you've taken all these precautions and oral sex was their only activity of "risk", so I think it is a false positive. When will you do another test? and
How long is your last sexual intercourse ?
with the information from the expert forum, I'm convinced that if you really only did protected the other times you will be fine.
I can imagine your stress ful period and my thoughts are with you.