Dear all,

I am 24 y.o. male student.
My first girlfriend, ~3 months after we started kissing, had high fever for several days, and was treated as having pneumonia, with antibiotics. Later after half-year she started having low fever constantly and was diagnosed a mononucleosis.

My current girlfriend, after two months of we started kissing, in June started having high fevers and developed an enlarged spleen after. Hospital diagnosis -- mononucleosis, she gradually but first vaguely started developing antibodies, now, after I was away from her for 3 weeks, last week she is having spleen retraction and less pain.
My mononucleosis (monospot, as well as HIV and hepatitis) tests are all negative.
I have done one more - mononucleosis antibodies test (IgM and IgG), which showed 0 concentration of IgM and IgG.

Can this be true that I am "clean" (although both girlfriends started having it) and I am susceptible to infection, although did not get it yet. I have chronical tonsilis for last 6 years (very easy to get tonsillitis after a cold blow to neck, but goes away quickly with JOX iodine-based spray) and I frequently catch cold, but maybe my immune system is still strong enough. And still I'm not a transmitter, as tests claim.

Is it also viable that I must restrain from mouth-to-mouth/oral-sex relations to my current girlfriend, as her family doctor suspects me re-infecting her over and over again without me actually getting ill and/or developing antibodies? Which would be a disaster I am feeling fine, no expressed fatigue or fevers, nor other symptoms. And have no idea, if I'm a carrier, or I am clean or a dunno-what-to-think..

Should I give in to my gf, so I could become sick and then develop immunitet against future middle-aged infections, which may wind up worse.
Or are the tests results false-negative, meaning that I do have chronical mononucleosis (with this mild tonsilitis ~2-3 times per year simptom in mind)?

Thank you very very much in explaining this case. Would really appreciate, as now I am completely lost...