I can't seem to gain strength!!!

[&o]
Hello everyone. 
I am just becoming so discouraged.  i have been working out for about a year and, although I have gained muscle and strength, it is moving at a very low speed. One of my goals is to be able to do pull-ups. I've heard about plateaus, but I feel like I often change my workout plans.  Maybe i don't stick to one long enough?
I tried circuit training, I've tried the basic 3 sets of 10-12, slipt days. 
I'm wondering if my nutrition has someting to do with it.  I think i'm sort of clueless as far as coming up with a nutritional plan for my goals. protein, carbs, fats, calories....i get so confused. I rarely eat fats except for nuts.  I would really benefit from a trainer slash nutritionist but can't afford one. Im 5'9 at 169lbs, could use to lose a couple. I also want to look more defined, which might be counteractive to getting stronger?
anyone know of any websites that can tell me exctly what I need to do, eat, workout to reach my goals?
I know i just unloaded a lot

This is a great web site for information.  Another to keep track of how much Protein, carbs and fat you take in is Fitday.com.  It's tought to gain strength and lose weight at the same time.  You should really pick which one you want to focus on first because trying to do both can be counter-productive.  In order to gain strength, you need to feed the body.  Uh, makes it hard to lose weight then! ;)   You may want to look at a 6 to 8 week goal of building on strength, then shoot for losing some weight, or "cutting" as you may hear it called.  BUT, don't stop lifting weights during the "cutting" phase.  Find a helpful (but  knowledgable)  friend at your gym who could possibly point you in the right direction for the amt of weight you should use.  Goal for building strength is to lift heavy weights that will fatigue you after the 5th or 6th rep.  So, for losing weight... go with a lighter weight (to maintain your muscle strength) with more repetitions. 6-10 ish.  Again, find someone local who can really help you. 
 
Diet is a huge part of strength gain.  You need to make sure you are taking in adequate amounts of Protein, carbs and fat.  The ratios vary from one person to the next.  What is right for one person may not be right for the next.  Typical ratio is 55 to 60% from Carbs, 20-25% protein and 15 -25% fat.  That is pretty tight.  Especially the fat.  I do 15% when "cutting" and 20- 25% for normal diet.  Again, everyone is different.  Typically, if you are not gaining strength, you may want to look at how much protein you are eating.  Fish and Chicken are good, quality foods to eat.  Adding a quality whey protein into your diet might be helpful too.  I have choc. protein in my oatmeal every morning...love it!
 
Keep reading and researching here.  Just remember, what works for one person may not be right for you.  Do your own research to back up any information you might be told, just to be safe!  Hopefully, I was helpful!  Good luck!

I will never be done learning.... 
ACSM cert. Personal Trainer
Long term goal: Maintain 13%
Currently: 9.5%