Welcome to our Forum.  I will be glad to comment.  The events you describe were entirely safe in terms of risk for HIV or other STIs. Kissing, even deep French kissing with exchange of saliva is not a risk for HIV and other STIs.  It is far more likely that your flu-like symptoms were due to some other cause such as the sorts of viral infections most people get from time to time, not from an STI of and sort.  Further the testing you have had is definitive and completely rules out the possibility of HIV related to the events you have described. 

1) is there any possibility for my results to change? (The tests that i fid was combo test)

No, your combo results are definitive and will not change.

2) how can i get over this anxiety?

I hope that my comments will help you to move forward.  Sometimes anxiety of this sort is related to a feeling of guilt or shame.  Nothing you have done is wrong or something you should be ashamed of.  If your anxiety persists, talking through things with a trained counselor may be helpful.

3) if it is not hiv what other reasons that can cause my symptoms

See above.  There are many possible causes of the sorts of symptoms you experienced.  In most cases, when they are caused by every day viral infections, they tend to go away by themselves without treatment and should not be a source of concern.  If your symptoms have persisted, I suggest that you seek evaluation by your own doctor.

I hope these comments are helpful. Take care.  EWH

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Thank you for your quick replay 

If your lymph nodes are swollen (and this should be confirmed by a doctor) they are not due to HIV.  You exposure was no risk and your test results are definitive.  You should work with your doctor to find an alternative, non-STD, non-HIV reason for your symptoms.  EWH---