I was like you when I did my first run, cause I didn't knew what attributes and perks to put my points into. I found even normal difficulty to be very hard and died often like you. But after reading about s.p.e.c.i.a.l, perks and weapons I now find even survival to be very easy. And I play a sneak character, witch is OP if you look at the sneak damage multipliers (up to 6.3X), I mostly just one shot kill almost everyone (for legendary I use criticals).
So, here is what I did to make the game easy. First of all, stay in those areas of the map where low level enemies span, you have the map above. At survival, enemies will be bullet sponges (until you get a good weapon) so for damage take either Gunslinger or Rifleman perks, depending on if you are gonna use snipers or pistols, investing in both is just wasting precious points. Then, take one level of Scrounger to have more bullets available and Gun Nut (or Science if you're into energy weapons mid to late game) to mod your weapons to have more damage, range and accuracy. Imagine getting across a rifle with a suppressor, ideal for stealth, but finding out that it does crappy damage - gun nut will make you get the most out of it.
Still you will want to find a weapon with good damage early on, getting the Overseer's Guardian till level 10 was a game changer for me. All that pick pocketing, stealing from buildings and scavenging to raise money for it was worth it, ot you can go raising money from settlements - mutfruits and purified water, or brewing and selling chems. If you want a suppressed rifle early on you will want to join the Railroad, do a few missions for them and then buy 'Tinker Tom Special'. Or if you are a pistol guy from the Railroad you can get the suppressed pistol 'The Deliverer'.
For defense: you don't need to put points in endurance or or get endurance perks to get more hp or to get tanky as the point of sneak is to almost never get caught and to clear entire areas from the shadows. Sneak perk helps a lot with this, get like 2 levels of it early on, at level 2 you will render all mines and traps useless. Light levels matters greatly, I noticed it is way harder to stay [hidden] during daylight, even in the shadows, in direct sunlight is almost impossible, so I recommend you do the killing at night time, if it's day time find a bed or a chair and wait. Even at night time avoid the lighted areas. You already have high agility so sneaking will be easier.
For sneaking damage: the Ninja perk as soon as possible to get the damage multiplier from sneak, and upgrade whenever possible. Also, the Sandman, if you have a suppressed weapon. With these 2 you will do like X5 damage when sneaking. Also, Deacon will give you some bonuses too if you max your affinity with him. You will want the [hidden] or [caution] at all times to benefit from these multipliers. If you find that in [cation] mode enemies start firing towards you, step aside left or right and back off a little. They are firing at where they think you are anyway. If you get the [danger] mode, only then they discovered you, so run back and take cover till they lose you again, tanking them is not a good idea as you don't have nor the hp or the perks to do that. The last level of sneak is just child's play...you will be able to sneak to just 2 meters from them, or just near touching distance if they are not looking in your direction. Even in power armor I do that. And also, the higher the sneak skill, the quicker you will go from [danger] to [caution] to [hidden] mode. Most of the time, I don't even get the [danger] status when clearing out a location. If you get into trouble though and get surrounded, get a shotgun and enter vats, then pop some Jet, this can happen with flying insects, mole rats, Supermutant hounds or radscorpions.
If you use vats often here is what you can do to have a easy game: http://www.gamesas.com/topic/1575192-dont-see-the-point-of-vats/page-4#entry24750592
Good luck.