From everything I've read most people who talk about how long after their last shot to get high are using IV heroin. In general, though, after one shot and based on everything I've read I think 35-40 days would be safe to get high again from pills. My experience is hard to relate as I was on it for 8 months and seem to be having a much longer period of effects than the average person.
I had a similar experience to you mood-wise, but it took a bit longer than a week for that to really set in, for me. Like I said above, I was on the shot for 8 months. It actually did really help with the cravings for me, but a lot of that could have been that I wanted to be clean (at the time) and psychologically knowing that I couldn't get high, even if I tried. It made the thoughts of using more fleeting and less obsessive. After maybe 2 months on the shot the side effects you described started to get to me, though. Depression, feeling "out of it" or disconnected, anxiety and agitation, loss of pleasure from regular activities. My need for some euphoric feeling started coming out in other ways; sex, spending/online shopping, food/overeating (put on a ton of weight), etc. The "addiction doctor" I went to for the detox and then the Vivitrol shots never went over any of these possibilities with me, despite that he should have per the Vivitrol packaging (which I never got to see any of the Vivitrol inserts because it goes straight to the doctor and he injects it and assumably throws away the rest). After about 5-6 months on the shot (3-4 months after the negative side effects became very noteworthy) I started wondering if these feelings (especially the depression/disconnected feeling) could be side effects of the Vivitrol (I'd had numerous tests and labs looking for the cause of the way I was feeling, yet I still hadn't done much research on Vivitrol at this point as everyone told me there was nothing bad about it) and asked the doctor before my injection one day. He quickly assured me that nothing I described was caused by Vivitrol and that I probably just really needed another shot (no joke) and quickly administered the shot and left before I could ask another thing. I don't think Vivitrol is bad or good, necessarily, but everyone should have all of the information to make an informed decision.