What to change / what am I missing?

Ok, I'm very new to all this so bare with me! I just started working out for really the first time since high school, ten years ago. I'm trying to eat better and have been trying to do the four to five small meals a day. I've never ate breakfast before but suprisingly this has been going well for me. I don't have a lot of weight to lose, about 15 pounds only due to my height, just need more toning up and getting rid of unhealthy habits. Anyways, I'm missing something with my snacks, for example, Monday I had a banana then a few almonds, half of a flat bread sandwich with turkey and hummus, then a sarge not cheese snack later in the day, this was all spread out. For dinner I was starving to death, after I worked out I was shaking like I was going to pass out. I obviously didn't eat enough during the day but I was so full, in fact I had to force myself to eat the cheese stick. So what am I missing? A particular nutrient? According to MFP my food during the day, before dinner, was about 500 calories total...do I need something with more calories? Thanks in advance fir the help, again I'm new so be nice