[EDIT: I just noticed I missed that you're already working out. My bad, sorry.]
I hear you. Those feelings are terrible.
I have some good mornings believing it will be okay but then get really down in the afternoon/evening. I don't want her back, I just want to get over her and move on with my life. I want to be happy again. When I think of her, I wan't my thoughts and feelings to be neutral, to not even care.
It's been 3 months and I've only felt marginal progress at best. In fact, I feel I may have even regressed. Is this "normal"? What is the timeline here? What can I expect at 6 months? 8 months? 1 year? When will I get out of this hell hole? I really need a big shot of hope. Thanks.
It's great that you've already noticed a pattern. I had a similar epiphany the other day and perhaps it will make you laugh. I came home from the fitness centre, where I had just enjoyed an energising workout and felt great, but as soon as I was back home, I suddenly missed my ex and felt like crying my heart out.
Turns out I was fatigued, dehydrated and hungry, and that was enough to push me over the edge. Humans are slightly more complicated thinking, feeling machines: neglect to oil or fuel one part, and the whole operation can come crashing down.
Since you notice things get worse in the afternoon, maybe your feelings correlate with the typical afternoon slump of low blood sugar and/or sleep deprivation. If you aren't doing it already, eating healthily on a regular schedule, exercising, and making sure you get enough sleep goes a long way in preserving your sanity and getting over the breakup. Exercise will also help with low moods, because (after the initial uphill struggle) exertion causes the release of dopamine. It also helps releasing pent-up aggression which seems to be stressing you. It sounds like stupid, run-of-the-mill advice, but as someone who has often been snatched from the claws of despair by a workout (despite not being naturally athletic), I can only recommend giving it a try.
Nice side effect, you'll start feeling better about yourself, and when you're ready, the ladies are bound to notice, too.
Apart from these things you can do yourself, do you have anyone you can talk to about the whole thing in real life?