Weight Gain-Eating Habits/Lifting, or both?

At the quickest, your body will gain muscle at the rate of about 1.5lbs/mo. So no, while you may be getting much stronger (gaining a couple pounds of muscle IS noticeable, especially on a runner's frame) you haven't packed on 6 pounds of muscle. More like 2, at best.

A gain like yours is most likely based on diet, especially hydration. You're probably hungrier (working out more) and hopefully have been making an effort to stay hydrated (as you should - again, working out more). These are both good.

Honestly, stop weighing yourself so often. Check in every week or so to make sure you're aware of any dramatic changes in body composition.

Thank you for the input. Do you have any eating tips other than drinkig lots of water. I am drinking a lot, but could do better.

The complusive weighing is a hrd thing to break. It stems from 7 years of being a wrestler before taking up running seriously.

Just from a training perspective you should consider extending your easy runs to more than 3-5miles and slowing down the pace. This will allow you to go further (burn more cals) instead of always doing shorter cut-down runs as well as recover. The weight may be water weight, although seeing as you weigh more in the mornings (after using the bathroom) this seems somewhat flawed. When I first began supplementing my running with a legitimate lifting program (30min-1hr of weight work) I too gained 2-3lbs however I always assumed this was due to water weight as I forced myself to drink 3 glasses of water at each meal and weighed myself towards the end of the day.

bump

Not sure what precisely you're looking for, but some other assorted thoughts that may be of use:

Distance runner types (and your 136lb starting weight suggests you fit this mold) are mostly ectomorphs. (In the weightlifting community we're sometimes called "hardgainers," literally because it is hard for us to make significant gains in muscle mass and are naturally lean). The benefit of this body type is a naturally high metabolism (how do you think we got this way?!), but this has implications for a proper diet, especially if you're looking to incorporate a beneficial lifting program into your routine.

Whereas traditional diets for those looking to gain muscle mass emphasize a comparatively high percentage of calories from lean proteins, you'll benefit more from simple (good! not sugar) carbohydrates and starches than a typical gymrat. That said, sufficient protein intake is necessary to actually realize any gains (in running or in lifting). Without it, you'll find your muscles depleted and tired, and you won't make any strength gains. Chicken is a pretty ideal source - preferable in many ways to red meats - and spinach is similarly protein rich. Use it as a base for your salads, it's way better than lettuce or even mixed greens. Eggs, obviously. Eat often.