positive weakly looks like a very old assay to detect hbsag, the old ones have a sensitivity of 5iu/ml or 0.5iu/ml, don t remember exactly but it is not sensitive enough, if you can find an abbott architet assay it has 0.05iu/ml sensitivity
retest to see if it was a mistake of assay or hbv infection on clearing phase or starting, if you have free tests i'd check for hbvdna pcr, hbcab, hbeag, hbeab, alt/ast too so you might have a clear idea of infection
What does it mean & what to do next? Is it any serious matter to take treatment?
--Test it again and post the result here.