It's quite possible - likely in my layman's view, that you have an infection that is waxing and waning, causing changes in the PSA level. A fluctuating PSA is a classic sign of infection, though it's possible there may also be cancer present.
If the same lab was used for the PSAs of 6.4 and 4.4, that's pretty strong evidence for an infection causing at least some of the elevation because PSA that is due to cancer continues to increase at a steady exponential rate as a thousand cells split into two thousand, two thousand to four thousand, four to eight, and so on. PSA that is due to cancer does not drop unless affected by some "treatment". (That "treatment" is sometimes what we eat or use as supplements.) Your PSA did not continue to rise; instead, it dropped, before going up again.
Free PSAs are also thrown off by infections - their results for infections often look like results for cancers. You might want to try the PCA3Plus test, which is not affected by infection. It has been described a number of times on this board, and you can find those instances by searching.
Take care and I hope this helps,