Okay so since you finished HT in 2014 your PSA has steadily climbed, which is not entirely unexpected as you still have a prostate which will produce small amounts of PSA. It doesn't seem to me that your levels are worryingly high yet but the rate at which it is rising is quite fast so my guess is that they were just warning you that if it goes too high too fast then you may need some more treatment. Ideally they would offer you a scan before deciding whether or not to start treatment again and to help inform which treatment to offer you.