Yeah, it would help if you like explained your build? Since its "your own unique build" like you said, and we can help improve it But with oak, anything goes really, as long as it has maxed penitence in it.

What is slowly coming to seem to work for me is a build much like yours--concentrating on DG buffs for the first few-to-several levels, then concentrating mostly on army buffs later on. Like you, the early game is harder than the late game. But what I do about this is--I just lay low during the early game, and try not to get killed. If enemy comes to me and I don't know I can win, I throw pent and run back to my towers. Minions I sometimes throw at him, sometimes throw elsewhere on the map to fight grunts to get me some gold.

If the opponent spends all his time chasing after me, he's getting as little exp/gold as I am so no problem. If he stops chasing me and kills grunts or gets flags, then that gives me time to kill grunts and get flags elsewhere.

This does yield the floor to the opponent a little more than I would hope for, giving him a little more experience than me in general. But once I've gotten to the "building up my army" phase of development, I find I seem to be able to make up for it.

 I don't have a level-by-level description of the build, but the idea is this. I get pent, then shield, then justice. I think the next pent comes up then, so that's when I get it. Then I get surge of faith. Next, soul power. (Yes, soul power. I find it more useful at this point to have the 20 extra DPS for my DG than having the three spirits from spirit ward I. Probably a better micromanager than me would find the spirits more useful.) Then Pent again. Then I follow this rule: Spirit ward, unless a new pent level is available, in which case get pent instead. If neither is available, then get a level of morale. I haven't figured out yet whether it's better to get morale or spirit frenzy at level 15. At level 20 there's one more power to choose, and I haven't decided what to get with it. One more shield just gets you one mor second per cast, which doesn't seem worth it. Adding one more to surge of faith might be worth it, since enemy creeps are more powerful by this point of course. Or you may want to hold off on a point or two of morale, or not get spirit frenzy at all, and instead invest further into the sheild  or surge lines.

first off, maybe i'm misinterpreting your build but i think it sounds like you're taking points in Soul Power that are effectively doing zilch for you because you don't have Raise Dead Banner. please see this guide for more information on how Soul Power works: http://forums.demigodthegame.com/350419

Oak is generally quite weak before level 5 or 6. i try to play around this by concentrating on flag caps and creep farming in uncontested lanes until i've got the requisite skills and equipment to start fighting other DGs effectively.

there are several ways to achieve this but i'm afraid none of them include the option to save your initial gold. you'll need to be getting either a bunch of Teleport Scrolls, a Wand of Speed, or the Teleport Charm favor item.

the other approach is to stock up on combat health and combat mana potions and harass early with Penitence and Shield.

you'll be able to make up for the gold in spades at level 5 when your combination of Surge of Faith and Divine Justice allows you to blast through creep waves at super speed. i really can't stress enough how important getting Surge at level 5 is though, if you wait until level 9 you won't be able to farm creeps fast enough to stay competitive.